UNWERSTTYgrCALIFORNIA 

COLLEGE  of  MINING 

DEPARTMENTAL 
LIBRARY 

•   *  • 

BEQUEST  OF 

SAMUELBENEDICrCHRlSTY 

PROFESSOR  OF 
MINING  AND  METALLURGY 

1885-1914 


AT  WORK. 


8.  B.  CHRISTY 

MANUAL  OF  ASSAYING 

GOLD,  SILVER,  COPPER, 

AND 

LEAD  ORES. 


WITH    ONE   COLORED    PLATE   AND   NINETY-FOUR 
ILLUSTRATIONS   ON    WOOD. 


BY  WALTER  LEE  BROWN,  B.Sc 

M 

SECOND    EDITION. 

THOROUGHLY  REVISED,  CORRECTED,  AND  AUGMENTED. 


CHICAGO:. 
PUBLISHED    BY    E.   H.   SARGENT   &   CO. 

1886. 


T  /V 

37 


.    f 

MININC*   t» 


COPYRIGHT, 

BY  WALTER  LEE  BROWN. 
A.D.    1886. 


I     KNISHT    &  LEOKARU 
" 


EXTRACT  FROM  PREFACE  TO  FIRST  EDITION. 


WHEN  I  entered  upon  the  task  of  preparing  this 
book,  it  was  with  the  idea  of  furnishing  a  guide  to 
those,  who,  having  had  no  previous  technical  or  es- 
pecially scientific  education,  desired  to  learn  some- 
thing of  the  practical  assaying  of  gold  and  silver  ores, 
and  in  whose  hands  I  could  place  no  work  that  could 
give  them  this  information  in  a  clear,  simple  and  thor- 
oughly detailed  manner,  and  unburdened  with  un- 
necessary matter. 

This  intention  I  have  tried  to  adhere  to  all  the  way 
through,  and  while  I  have  added  other  information 
which  was  pertinent,  I  have  kept  such  increase  in  an 
appendix,  so  that  the  body  proper  of  the  work  con- 
tains the  real  subject  matter. 

It  is  my  sincere  belief  that  there  is  no  book  in  the 
English  language  on  the  subject  of  assaying  which 
occupies  the  space  that  this  little  manual  tries  to  fill. 

A  number  of  such  publications  fail  to  meet  the 
want,  on  account  of  their  antiquity,  they  having  been 
written  some  thirty  years  ago  ;  hence  their  methods, 
apparatus,  etc.,  are  not  suited  to  the  assayers  of  to- 
day. Others  are  either  more  suitable  as  books  of 
reference,  or  do  not  give  sufficient  detail  for  the  inex- 
perienced. 

It  is  this  latter  fault  I  have  carefully  endeavored 
to  avoid,  and  perhaps  have  gone  to  the  other  extreme. 
At  all  events,  I  have  tried  to  give  here  in  print  the 


PREFA  CE. 


precise  instruction  which  I  have  previously  imparted 
orally  to  my  students.  Those  who  may  choose  to 
criticise,  will  remember  for  whom  this  hand-book  is 
written. 

I  wish  to  publicly  thank  the  following  gentlemen 
who  have  very  kindly  aided  me  in  my  work  with 
valuable  information:  Mr.  S.  A.  Reed,  Irwin,  Colo.; 
Mr.  A.  H.  Low,  Assayer  of  the  Boston  and  Colorado 
Smelting  Works,  Argo,  Colo.;  Mr.  C.  Boyer,  Assayer 
of  the  U.  S.  Branch  Mint,  Denver,  Colo.;  Mr.  M.  G. 
Nixon,  Engineer,  and  Mr.  R.  G.  Coates,  both  of 
Chicago. 

March,  1883. 


PREFACE  TO  THE  SECOND  EDITION. 


So  many  words  of  praise,  both  from  the  press  and 
private  individuals,  greeted  the  first  edition  of  this 
work,  that  I  feel  encouraged  to  put  forth  a  second  and 
greatly  improved  edition,  which  will  not  contain  the 
faults  that  have  been  pointed  out  to  me  as  existing  in 
the  first. 

The  salient  features  of  the  new  comer  are  increase 
in  matter  from  318  to  488  pages;  the  stating  of  all 
charges  in  assay  tons,  grammes,  and  grains  ;  detailed 
charges  in  the  scorification  process  ;  full  notes  on  the 
colors  and  appearances  of  the  scorifiers  (with  a  col- 
ored plate)  and  cupels  after  work  ;  the  expansion  of 
the  crucible  process  from  nine  to  almost  ninety  pages  ; 
more  complete  articles  on  the  assay  of  gold  and  silver 
bullion,  and  the  volumetric  analysis  of  copper  ores  ; 
and,  finally,  the  issuance  of  the  book  in  flexible  covers. 

For  the  idea  of  the  oxidizing  powers  of  ores  which 
I  have  developed  in  the  notes  on  the  crucible  process, 
I  am  indebted  to  Aaron's  Assaying. 

Whatever  appears  in  this  edition  extracted  from 
the  following  authorities,  is  given  with  the  full  and 
written  permission  of  the  authors,  editors,  or  owners  of  the 
copyright,  as  the  case  may  be  :  Mitchell's  Manual  of 
Assaying,  Kustel's  Roasting  of  Gold  and  Silver  Ores, 
Aaron's  Assaying,  Chapman's  Furnace  Assay,  and 
Hank's  Fourth  Annual  Report  as  the  State  Mineralo- 
gist of  California. 

Besides  for  that  which  I  have  incorporated  from  the 


8  PREFACE. 


above-mentioned  sources,  I  wish  to  give  thanks  to  the 
following  gentlemen  :  to  Mr.  J,  C.  Jackson,  my  suc- 
cessor in  business  in  Chicago,  for  illustrations  of  a 
permanent  furnace,  and  particularly  for  the  neat  and 
characteristic  frontispiece  ;  to  Mr.  F.  E.  Fielding,  As- 
sayer,  Virginia  City,  Nev.,  for  valuable  notes  on  the 
assay  of  gold  bullion  and  volumetric  analysis  of  cop- 
per ores  ;  and  to  Mr.  G.  H.  Ellis,  for  the  careful  work- 
ing out  of  the  qualitative  schemes. 

WALTER  LEE  BROWN. 
Aurora,  111.,  Oct.  i,  1886. 


CONTENTS. 


PART    I. 
APPARATUS  AND  RE-AGENTS. 

CHAPTER  I. 
APPARATUS  USED  IN  ASSAYING. 

IMPLEMENTS  FOR  PULVERIZING,  SAMPLING,  ETC.,           .         .  20 

SCALES  AND  BALANCES,    .__..__  36 

WEIGHTS,            .        _         . 59 

FURNACES, 64 

FURNACE  TOOLS,         ........92 

APPARATUS  USED  IN  THE  FURNACE,          ....  102 

APPARATUS  OF  GLASS  AND  PORCELAIN,         .        .         .         _  in 

MISCELLANEOUS  APPARATUS,  .         .         .         .         .         .  116 

CHAPTER  II. 
RE-AGENTS  USED  IN  ASSAYING. 

DRY  RE-AGENTS  FOR  ASSAYING,  .....  128 

WET  RE-AGENTS  FOR  ASSAYING,       .....  142 

RE-AGENTS  FOR  ANALYSIS,  _.....  144 

MISCELLANEOUS, 152 

CHAPTER  III. 
TESTING  OF  RE-AGENTS. 

I.    TESTING  OF  LITHARGE  FOR  SILVER,      ....     154 

II.    TESTING  OF  GRANULATED  LEAD  FOR  SILVER,    _         .          158 

III.    TESTING  OF  SHEET  LEAD  FOR  SILVER,  ...     160 

9 


IO  CONTENTS. 


IV.    DETERMINATION  OF  THE  REDUCING  POWERS  OF  REDUC- 
ING AGENTS,  __.._..     161 
V.    DETERMINATION  OF  THE  OXIDIZING  POWER  OF  NITRE 

(NITRATE  OF  POTASH), 162 

PART    II. 
ASSAYING.      . 
CHAPTER  I. 
GOLD  AND  SILVER  ORES. 

OCCURRENCE,          _.._....         167 

ASSAY, 170 

I.    PREPARATION  OF  THE  SAMPLE,  ...          171 

II.     SCORIFICATION  PROCESS,  .....       l8l 

a.  Preparation  of  Charge,  183;  b.  Scorification, 
194;  c.  Cupellation,  200;  d.  Weighing  the 
Gold  and  Silver  Bead,  209;  e.  Parting,  210; 
f.  Inquartation,  214;  g.  Weighing  the  Gold 
Residue.  215;  h.  Calculations,  216. 

III.    CRUCIBLE  PROCESS, 217 

Preliminary,  217;  Roasting,  259;  Methods  of 
the  Crucible  Assay,  264;  Preparation  of  the 
Charge,  267;  Running  the  Crucibles  in  the 
Fire,  273;  General  Charges,  276;  Special 
Charges  and  Directions,  282. 

CHAPTER  II. 
COPPER  ORES. 

OCCURRENCE 304 

ASSAY. 305 

I.    METHOD  FOR  NATIVE  COPPER,       ....  306 

II.    METHOD  FOR  OXIDES  AND  CARBONATES  OF  COPPER,  307 

III.    METHOD  FOR  SULPHIDES  OF  COPPER,     .         .         .  307 


CONTENTS.  I  I 


CHAPTER   III. 

LEAD  ORES. 

OCCURRENCE,          ..._.._.  311 

ASSAY, 312 

I.    METHODS  FOR  GALENA,       .  312 

II.    METHODS  FOR  OXIDES  AND  CARBONATES,         .         .  320 


APPENDIX. 

SECTION  I. 

SPECIAL  METHODS. 

I.    ASSAYING  OF  THE  VARIOUS  MINERALS  CONTAINED  IN 

AN  ORE,  _ 327 

II.    ASSAYING  OF  ORES  CONTAINING  FREE  GOLD  OR  FREE 

SILVER, _  329 

III.  ANALYSIS  OF  COPPER  ORES,       .  333 

IV.  AMALGAMATION  ASSAY  OR  LABORATORY  MILL  RUN,  351 
V.    PAN  TEST  FOR  GOLD  ("  PANNING  "),           _  355 

VI.    CHLORINATION  ASSAY  OF  GOLD  ORES,  .         .        _  364 

VII.    CHLORINATION  TEST  FOR  SILVER,      ....  367 

VIII.  -THE  ASSAY  OF  GOLD  BULLION  AND  SILVER  BULLION,  369 

IX.    THE  ASSAY  OF  BASE  BULLION,  ....  404 

X.    QUALITATIVE  TESTS;  CARBONATES,  SULPHATES,  SUL- 
PHIDES, TELLURIDES,  COPPER,  IRON,  LEAD,  MAN- 
GANESE, SILVER,  .......  408 

XI.    BRIEF  SCHEME  FOR  SILICA,  IRON,  AND  MANGANESE,  413 

XII.    DETERMINATION  OF  MOISTURE  IN  AN  ORE,  415 

XIII.    DETERMINATION  OF  SULPHUR  IN  PYRITES,      .         .  416 

SECTION   II. 
LISTS  AND  REFERENCES. 

LIST  OF  THE   PRINCIPAL   GOLD   MINERALS   FOUND  IN  THE 
UNITED  STATES, 417 


1 2  CONTENTS. 

MINERALS  LIKELY  TO  CARRY  GOLD,  ....  418 
LIST  OF  THE  PRINCIPAL  SILVER  MINERALS  FOUND  IN  THE 

UNITED  STATES, 418 

MINERALS  LIKELY  TO  CARRY  SILVER,  .        .        .         .421 

LIST  OF  THE  PRINCIPAL  COPPER  MINERALS  FOUND  IN  THE 

UNITED  STATES, 422 

LIST  OF  THE  PRINCIPAL  LEAD  MINERALS   FOUND  IN   THE 

UNITED  STATES, 425 

LIST  OF  USEFUL  BOOKS  ON  SUBJECTS  MORE  OR  LESS  CON- 
NECTED WITH  ASSAYING:  GENERAL  SCIENCE;  GENERAL 
CHEMISTRY;  CHEMICAL  TECHNOLOGY;  REFERENCE  BOOKS 
ON  CHEMISTRY;  TEXT-BOOKS  ON  THEORETICAL  CHEMIS- 
TRY; GENERAL  QUALITATIVE  ANALYSIS;  GENERAL  QUAN- 
TITATIVE ANALYSIS;  SPECIAL  QUANTITATIVE  ANALYSIS; 
VOLUMETRIC  ANALYSIS  ;  LABORATORY  MANIPULATION  ; 
GEOLOGY;  MINERALOGY;  BLOW-PIPE  ANALYSIS;  METAL- 
LURGY AND  MINING;  ASSAYING;  METRIC  SYSTEM  — 
WEIGHTS  AND  MEASURES;  MINING  LAW,  ...  428 

PLAN  FOR  ASSAY  LABORATORY,  ' 437 

FORM  FOR  CERTIFICATE  OF  ASSAY 438 

OUTFIT.  ASSAYING,          .  ..        .        .         .         -         439 

OUTFIT,  BLOW-PIPE, -     44* 

SECTION   III. 

TABLES. 

MULTIPLICATION  TABLE  FOR  GOLD  AND  SILVER,  _  .  443 
TABLE  OF  VALUES  OF  GOLD  AND  SILVER,  ....  444 
TABLES  OF  WEIGHTS:  AVOIRDUPOIS;  TROY;  APOTHECARIES'; 

FRENCH  OR  METRIC  SYSTEM,  .  445 

EQUIVALENTS  OF  SOME  OF  THE  ENGLISH  AND  FRENCH 

WEIGHTS -  449 

ASSAY -TON  EQUIVALENTS  IN  GRAMMES,  TROY  GRAINS,  AND 

TROY  OUNCES, 45° 

INDEX,  461 


INTRODUCTION. 


In  our  present  state  of  knowledge  we  be- 
lieve all  matter  to  be  composed  of  one  or 
more  elements  or  original  simple  substances. 

These  elements  are  considered  to  be  sev- 
enty in  number.  Certain  of  them  have  what 
we  may  call  a  commercial  importance.  (See 
Introduction  to  Attwood's  Blow-pipe  Assay- 
ing.) They  are  as  follows,  the  metals  being 
in  italics: 

1.  Aluminium.  16.  Gold. 

2.  Antimony.  17.  Hydrogen. 

3.  Arsenic.  18.  Iodine. 

4.  Barium.  19.  Iridium. 

5.  Bismuth.  20.  Iron. 

6.  Boron.  21.  Lead. 

7.  Bromine.  22.  Lithium. 

8.  Cadmium.  23.  Magnesium. 

9.  Calcium.  24.  Manganese. 
10.  Carbon.  25.  Mercury. 
n.  Chlorine.  26.  Molybdenum. 

12.  Chromium.  27.  Nickel. 

13.  Cobalt.  28.  .Nitrogen. 

14.  Copper.  29.  Oxygen. 

15.  Fluorine.  30.  Palladium. 


14  INTRODUCTION. 

31.  Phosphorus.  39.  Tin. 

32.  Platinum.  40.  Titanium. 

33.  Potassium.  41.  Tungsten. 

34.  Silicon.  42.  Uranium. 

35.  Silver.  43.  Vanadium. 

36.  Sodium.  44.  Z/MT. 

37.  Strontium.  45.  Zirconium. 

38.  Sulphur. 

Some  of  the  above  are  valuable  in  them- 
selves, others  in  combination. 

The  remainder  of  the  elements,  which  have 
no  especial  value  excepting  perhaps  as  curi- 
osities, are  : 

1.  Ccesium.  14.  Rhodium. 

2.  Cerium.  15.   Rubidium. 

3.  Columbium.  16.  Ruthenium. 

4.  Davyum.  17.   Samarium. 

5.  Decipiiim.  18.   Scandium. 

6.  Didymium.  19.   Selenium. 

7.  Erbium.  20.    Tantalum. 

8.  Gallium.  21.  Tellurium. 

9.  Glucinum.  22.    Thallium. 
10.  Indium.  23.    Thorium. 
n.  Lanthanum.                       24.    Ytterbium. 

12.  Norwegium.  25.    Yttrium. 

13.  Osmium. 

Besides  the  seventy  elements  above  enu- 
merated, there  are  some  ten  or  more  ex- 
tremely rare  metals  (actinium,  gadolinium, 
germanium,  helium,  holmium,  idunium,  ilme- 


IN  TR  OD  UC  TION.  I  5 


nium,  mosandrium,  neptunium,  philippium, 
terbium,  thulium,  etc.),  whose  existence  is 
not  yet  quite  satisfactorily  proven. 

In  order  to  ascertain  the  value  of  an  ore,  it 
is  necessary  to  determine  the  percentage  of 
the  metal  or  metals  which  it  contains. 

This  is  the  first  thing  to  be  done — an  after 
consideration  is  the  question  of  the  presence 
of  other  ingredients  which  may  injuriously 
affect  the  value  of  the  ore  or  product. 

There  are  two  general  methods,  known 
respectively  as  assaying -&K&  analysis,  whereby 
we  may  test  an  ore  to  learn  its  composition. 

A  comprehensive  definition  of  assaying  is 
to  call  it  that  branch  of  exact  science  which 
enables  us  to  find  out  of  what  a  substance  is 
composed  and  the  proportions,  by  means  of 
dry  re-agents  and  heat. 

On  the  other  hand,  analysis  is  that  branch 
which  effects  the  same  results  mainly  by  the 
use  of  wet  re-agents,  with  or  without  the  aid 
of  heat. 

In  spite  of  this  distinction,  wet  assays,  as 
opposed  to  dry  or  fire  assays,  are  continually 
spoken  of  ;  still,  to  be  as  consistent  as  possi- 
ble, the  terms  assaying  and  analysis,  as  defined 
above,  will  be  used  throughout  this  work. 


j  6  IN  TR  OD  UC  TJON. 

The  greater  number  of  the  processes  given 
in  this  little  book  come  under  the  former 
heading,  while  analysis  proper  is  employed 
in  only  a  few  cases. 

The  following  metals  are  sought  for  in  ores 
by  assaying  :  antimony,  bismuth,  cobalt,  cop- 
per, gold,  iron,  lead,  nickel,  platinum,  silver, 
tin  and  zinc. 

It  is  the  object  of  this  manual  to  treat  only 
of  gold,  silver,  copper  and  lead.  For  informa- 
tion concerning  the  assaying  of  the  remaining 
metals  just  mentioned,  the  student  must  seek 
it  on  page  434,  among  the  various  works  on 
assaying  there  quoted. 


PART  I. 
APPARATUS  AND  RE-AGENTS. 


MANUAL  OF  ASSAYING, 

PART    I. 
APPARATUS    AND    RE-AGENTS. 


CHAPTER    I. 
APPARATUS   USED   IN   ASSAYING. 

IT  is  as  true  of  the  art  of  assaying  as  of 
any  other,  that  "good  work  requires  good 
tools."  While  many  of  the  latter  can  be 
dispensed  with  by  the  skilled  assayer,  it  is 
often  convenient,  if  not  absolutely  necessary, 
for  the  unskilled  to  have  the  best  utensils  for 
the  work  required. 

I  shall  therefore  give  an  exhaustive  list  of 
apparatus  needed  for  the  processes  herein 
described,  but  shall  try  to  avoid  mentioning 
many  implements  which  are  not  essential. 


2Q  MANUAL    OF  ASSAYING. 

« 

IMPLEMENTS    FOR    PULVERIZING,    SAMPLING,   ETC. 

Iron  Mortars  and  Pestles. — Two  sizes  of 
mortars  are  handy,  a  large  one  1 1  inches  in 
diameter,  and  weighing  with  pestle  about  35 
pounds  (2  gallons  capacity),,  and  a  smaller 
one  of  5  inches  diameter  and  7  pounds  weight 
gallon  capacity).  Instead  of  both,  a 
medium  size,  8  inches  diameter,  in 
weight  about  19  pounds  (i  gallon 
capacity),  may  be  employed.  They 
may  be  either  bell  or  urn-shaped. 
FlG-  *•  Care  should  be  taken  to  remove 

all  ore  from  the  mortars  after  grinding.  Gen- 
erally an  old  towel,  rag,  or  even  paper,  will 
suffice  to  do  this,  but  occasionally  washing 
must  be  resorted  to.  Dry  thoroughly  after 
the  latter  operation.  Triturating  with  dry 
sand  often  answers  the  purpose.  When  not 
in  use  let  the  mortars  rest  mouth 
downward. 

Mortars    of    various    sizes    can 
also  be  obtained  with  two   oppo- 
FIG.  2.        sitely  situated  projections,  to  serve 


APPARATUS    USED   IN  ASSAYING. 


21 


either  as  handles  for  carrying,  or  as  trunnions 
for  turning  over  and  dumping  contents.  Fig. 
2  represents  this  pat- 
tern. 

To  ease  the  labor 
of  lifting  a  heavy 
pestle,  an  arrange- 
ment similar  to  that 
shown  in  fig.  3  is 
recommended.  This 
particular  form  is 
that  which  was  in 
use  in  my  own  lab- 
oratory, where  it  al- 
ways gave  satisfac- 
tion. 

The  spring  does 
not  perceptibly  add 
to  the  force  required 
to  strike  a  crushing 
blow,  but  does  ma-  .  FIG.  3. 

terially    aid    in    lifting    the    pestle.      It    (the 
spring)  is  1 8  inches  long  (when  unstretched) 


22  MANUAL    OF  ASSAYING. 

in  coils  of  if  inches  diameter,  made  of  the 
best  steel  of  \  inch  diameter,  and  painted 
with  asphalt  black  as  a  protection  against 
rust.  It  is  connected  to  the  bracket  by  a 
strong  and  flexible  cord.  The  supporting 
bracket  or  hook  is  of  \  inch  malleable  iron. 
The  distance  of  the  eye  from  the  wall  I  have 
made  13  inches,  but  it  can,  of  course,  vary  to 
suit  the  circumstances.  When  not  in  use  do 
not  keep  the  spring  taut,  but  let  the  lower 
end  be  hung  loosely  from  a  hook  in  the  wall. 

Instead  of  the  above  contrivance,  a  spring- 
board of  hickory,  3  inches  wide,  \  to  i  inch 
thick,  and  10  feet  long,  the  further  end  firmly 
fastened,  the  free  end  connecting  by  a  strong 
rope  with  the  pestle,  will  do. 

Any  assay  laboratory,  whether  permanent 
or  transient,  will  require  at  least  one  of  the 
three  sizes  of  mortars  specified.  For  fixed 
laboratories,  and  where  the  quantity  of  ore  to 
be  crushed  is  considerable,  a  very  large  mor- 
tar, 1 8  inches  deep  and  12  inches  wide 
(weight  about  150  pounds),  to  stand  on  the 


APPARATUS    USED  IN  ASSAYING.  2$ 

floor,  is  very  valuable.  The  pestle  accom- 
panying it  is  3  feet  long,  and  weighs  about 
1 8  pounds.  The  striking  end  is  usually  flat- 
tened out  to  a  width  of  from  4  to  6  inches  to 
cover  more  ore  at  a  blow,  and  also  to  prevent 
the  flying  out  of  the  crushed  material.  To 
use,  the  assayer  stands  over  the  mortar, 
grasping  the  pestle  with  both  hands. 

The  spring  or  spring-board  arrangement 
can  likewise  be  applied  to  the  pestle  of  this 
mortar. 

To  prevent  pieces  of  ore  which  are  being 
crushed  in  the  mortar  from  flying  out,  it  is  a 
good  plan  to  cut  a  piece  of  wood,  pasteboard 
or  tin  of  a  circumference  somewhat  larger 
than  that  of  the  top  of  the  mortar,  with  a 
hole  in  the  centre  large  enough  to  admit  of  a 
little  play  to  the  pestle,  and  to  lay  this  on  top 
of  the  mortar  while  at  work. 

Crushers. — These  are  intended  to  take  the 
place  of  the  mortar  and  pestle  for  crushing 
comparatively  large  quantities  of  ores.  For 
small  samples  the  mortar  will  do  very  well, 


MANUAL    OF  ASSAYING. 


but  for  say  20  pounds  and  upward,  some  sort 
of  a  crusher  will  be  a  desideratum.  Espe- 
cially will  it  be  needed  in  a  large  assay  labo- 
ratory. 

There  are  quite  a  number  of  hand  crushers 
in  the  market  intended  solely  for  laboratory 
purposes,  such  as  the  Alden,  Blake,  Forster, 
Lipsey,  etc. 


FIG.  4. 


Among  the   best   is  the   Lipsey,   which   is 
represented  in  full  in  fig.  4,  and  in  section  in 


APPARATUS    USED  IN  ASSAYING. 


Fie,  5. 

fig.  5.     It   can   be   turned    either  by  hand  or 
power. 

For  laboratories  where  say  half  a  ton  or 
so  of  ore  is  frequently  to  be  crushed,  I 
can  heartily  recommend  Krom's  Laboratory 
Crusher,  shown  in  fig.  6.  It  requires  power. 
To  insure  its  cleanliness,  run  through  it,  just 


26 


MANUAL    OF  ASSAYING. 


FIG.  6. 


APPARATUS    USED   IN  ASSAYING.  2J 

before  using,  a  lot  of  old  crucibles  and  scori- 
fiers,  or  some  worthless  ore  or  rocks. 

Fig.  7  illustrates  the  Bosworth  Crusher  for 
laboratory  use,  and  which  runs  by  either  hand 
or  power.  It  has  been  highly  praised. 


The  value  of  whatever  crusher  is  employed 
will  depend  mainly  upon  the  ease,  rapidity, 
and  thoroughness  with  which  it  can  be  cleaned. 

Certain  special  apparatus,  as  hand-stamps 
and  pulverizers,  must  be  left  to  the  necessi- 
ties and  preferences  of  the  individual  assayer. 


28 


MANUAL    OF  A  SSA  YING. 


Pulverizing  Plate  and  Rubbers. — These  are 
so  useful  and  convenient  that  they  can  hardly 


FIG.  8. 

be  dispensed  with  ;  in  fact,  if  much  assaying 
is  to  be  done,  they  will  become  absolutely 
necessary.  They  are  represented  in  fig.  8. 
The  iron  plate,  which  should  be  perfectly 
true  and  have  a  smooth  surface,  is  made  of 
varying  dimensions,  as  12x12,  18x24,  23x24, 
24x24,  24x30  and  24x36,  in  inches.  It  is 
made  with  no  protecting  rims,  or  with  rims  at 
the  sides  only  (as  figured),  or  with  a  rim  at 
each  side  and  at  one  end,  leaving  one  end  open. 
In  some  cases  the  side  rims  gradually  shallow 


APPARATUS    USED  IN  ASSAYING.  29 

from  the  back  to  the  front.  The  size  I  use, 
and  with  which  I  have  no  fault  to  find,  is 
18x24  inches  (inside  measurement);  thickness 
of  bottom,  i  inch  ;  rims,  f  inch  wide  and  i-J- 
inches  high  ;  weight,  150  pounds. 

(The  only  improvement  I  can  suggest  would 
be  to  have  the  back  corners  rounded  instead 
of  being  right  angles,  in  order  to  facilitate 
the  removal  of  pieces  of  ore  and  the  dust. 
Or  the  rims  might  be  cast  at  an  angle  of  say 
30°  instead  of  being  perpendicular  to  the 
surface.) 

The  rubber,  rocker,  pulverizer,  grinder, 
muller,  bucking-hammer  (by  which  various 
names  it  is  known),  to  go  with  above  plate, 
is  8  inches  long  and  4  wide  ;  thickness  at 
ends,  i^  inches;  in  centre,  2-J- ;  surface  true 
and  smooth  ;  weight  about  14  pounds.  Other 
rockers  made  are,  in  general  dimensions,  4x5, 
4X5-J-,  4x6,  6x7  and  8xio  inches. 

An  axe-handle  is  fitted  into  .the  socket  on 
top  of  rocker,  and  then  it  is  ready  for  use. 

The  operation  of  grinding,   or  rubbing,   or 


30  MANUAL  OF  ASS  A  YING. 

pulverizing  is  described  under  the  treatment 
of  the  ores  in  Part  II. 

When  a  very  hard  ore  is  to  be  pulverized, 
it  can  much  more  quickly  be  finished  with  an 
8X10  rocker,  weight  60  pounds.  The  addi- 
tional weight  and  greater  width  have  a  marked 
effect.  An  intermediate  size  of  about  30 
pounds'  weight  would  not  be  amiss. 

The  plate  can  be  placed  upon  a  stout  table, 
but  it  will  be  better  in  the  long  run  to  have 
constructed  for  it  a  special  and  substantial 
frame-work,  as  the  long  continued  rubbing  on 
the  plate  will  eventually  dislocate  any  ordi- 
nary table.  The  frame  can  have  vertical  legs 
as  shown  in  the  cut,  or  can  have  them  set 
with  an  angle  of  a  few  degrees'  spread  at  the 
floor  to  which  they  should  be  firmly  screwed, 
using  L-shaped  plates  of  iron  as  the  holders. 
Additional  strength  may  be  secured  by  insert- 
ing a  thick  shelf  at  about  six  inches  from  the 
floor,  and  this  can  serve  as  a  resting  place  for 
the  mortars  where  they  will  be  out  of  the  way. 

In  Mr.  S.  A.  Reed's  laboratory  the  plate  is 


APPARATUS    USED  IN  ASSAYING.  31 

set  at  an  angle  inclining  toward  the  operator 
so  as  to  allow  of  more  effective  pressure  at 
the  bottom,  and  slipped  under  the  front  end 
of  the  plate  is  a  trough  or  gutter  of  sheet-tin 
or  zinc,  as  shown  in  the  figure.  Its  object  is 
to  catch  any  particles  that  may  roll  down  the 
plate,  and  after  the  sample  has  been  pulver- 
ized, the  whole  of  the  powder  is  brushed  down 
into  it.  The  trough  is  easily  detached  from 
the  plate  and  its  contents  can  then  be  brushed 
into  a  sieve.  This  simple  device  may  replace 
one  of  the  zinc  sifting  pans  spoken  of  else- 
where. 

Sample  Shovels. — A  pitch-fork  with  each  tine 
transformed  into  a  narrow  trough  would  give 
a  fair  idea  of  the  appearance  of  one  of  these 
shovels.  A  better  form  consists  of  two  troughs 
from  four  to  six  inches  deep  united,  with  a 
space  between,  and  provided  with  a  long  han- 
dle. These  implements  are  more  needed  in 
sampling  works  proper  than  in  the  ordinary 
laboratory. 

Samplers  (also  known  as  dividers).  —  One 


32  MANUAL    OF  ASS  A  YING. 

form  of  these  is  shown  in  fig.  9, 
and  consists  of  a  frame  with 
partitions  running  lengthwise 

FIG.  9 .  it- 

at  equal  distances  apart,  and 
having  each  alternate  space  covered  at  the 
bottom.  It  is  made  of  tin  or  copper,  and  it 
is  well  to  have  three  sizes.  A  second  pattern 

is  represented  in 
fig.  10.  The  first 
form,  however,  is 
preferred,  as  being 
FIG.  10.  more  durable. 

To  use  either,  sprinkle  over  and  across  the 
broken  ore  to  be  sampled,  and  retain  that 
which  catches  in  the  troughs, 

A  pulp  is  sometimes  sampled  by  the  use  of 
a  sampler  of  tin,  having  troughs  \  inch  in  dia- 
meter and  T3T  inch  apart.  To  use,  sprinkle  the 
sample  across,  over  a  piece  of  clean  paper, 
and  separate  that  which  goes  between  the 
troughs  from  that  which  catches  in  them.  Af- 
ter putting  aside  the  latter  portion,  sprinkle 
across  the  sampler  the  former  portion,  and  so 


APPARA  TUS  USED  IN  ASS  A  YING. 


33 


continue   until  a  quantity  is   obtained  about 
sufficient  for  assay. 

Fig.  1 1  illustrates  the  Richards  Pulverizer 
or  laboratory  "arrastre."  It  may  be  used  in 
place  of  the  grinding  plate,  or  for  the  amal- 
gamation of  small  quantities  of  ores.  (See, 


FIG.  ii. 

in  appendix,  "  amalgamation  assay.")  It  is 
of  cast  iron,  and  is  simply  a  mortar  with  its 
pestle  revolving  on  a  spindle  and  turned  by  a 
crank.  The  mortar  has  a  trunnion  attach- 
ment to  aid  in  dumping  its  contents.  Its 
diameter  is  8^  inches,  weight  65  pounds,  and 


34  MANUAL    OF  ASSAYING. 

price  $10.     The  same  apparatus,  without  the 
trunnion  attachment,  is  also  procurable. 

Sieves. — A  sieve  of  80,  90  or  100  meshes  to 
the  linear  inch  is  necessary.  Such  sieves  are 
furnished  of  5,  6,  7,  8,  9,  10,  12  and  15  inches 
diameter  (6  to  8  inches  is  a  good  size),  of 
copper  or  brass  wire  in  a  wooden  frame. 
Those  composed  of  horse  hair  are  apt  to 
deteriorate.  The  box-sieve  of  tinned  iron, 
consisting  of  a  sieve  (of  80  to  100  mesh) 
with  tightly  fitting  bottom  to  catch  all  the 
sifted  material,  and  cover  to  retain  the  dust, 
is  a  valuable  implement. 

A  sieve  which  is  better  than  the  ordinary 
wood-bound  pattern  is  one  that  is  pressed  or 
moulded  out  of  the  sheet  gauze,  and  with  no 
wooden  rim  to  retain  pieces  of  an  assay  which 
may  afterward  fall  out  to  contaminate  a  suc- 
ceeding assay.     It  would  require  but 
little  of  a  rich  ore  to  make  a  worthless 
one  appear  valuable  by  the  above  acci- 
dent.     Fig.  12  shows  the  idea. 
If  the  system  of  sieving  and  sampling  that 


APPARATUS    USED   IN  ASSAYING.  35 

I  speak  of  under  the  sampling  of  ores  is 
adopted,  there  will  be  required  a  further  set 
of  four  sieves  of  2,  4,  8,  and  16  meshes  re- 
spectively, each  10  inches  in  diameter,  and 
with  frames  of  wood  3^  inches  deep. 

A  4O-mesh  sieve  is  useful  for  sieving  cer- 
tain chemicals,  and  two  common  flour  sieves 
are  wanted  for  bone-ash  and  granulated  lead. 

Zinc  Sifting  Pans.     Fig.  13. — These  will  be 


FIG.  13. 

found  convenient,  and  are  better  than  paper 
for  sifting  over.  A  pair  is  necessary,  the 
material  sheet  zinc.  Length  in  full  31  inches, 
of  body  25  inches,  of  neck  6  inches,  width  of 
body  12  inches,  of  neck  2  inches,  height  of 
rim  2f  inches,  with  upper  edge  turned  over 
heavy  iron  wire. 

Spatulas   and  Spoons. —  By    a    spatula   we 
mean  an  instrument  shaped  somewhat  like  a 


36  MANUAL   OF  ASSAYING. 

table-knife  (fig.  14),  and  used  for  mixing 
paints,  ores,  charges,  etc.  It  may  be  of  iron, 
steel,  copper,  platinum,  silver,  ivory,  horn, 
porcelain  or  glass.  A  large  one  of  steel 
or  iron  (such  as  painters  use),  length  in  full 
loj  inches,  blade  5!  inches  long  by  i^ 
wide,  is  a  very  good  size  for  mixing  ores 
and  crucible  charges.  For  weighing  out  ores 


FIG.  14. 

and  mixing  scorification  charges,  a  smaller 
one  of  steel,  length  6  inches,  blade  3X|  inch 
is  useful. 

Two  or  three  horn  spoons,  with  or  without 
handles,  are  serviceable  for  various  purposes. 

SCALES    AND    BALANCES. 

Two  balances  will  be  sufficient  for  the 
ordinary  work  of  the  assayer ;  a  small  one 
for  weighing  fluxes,  ores,  lead  buttons,  cupels, 
etc.,  and  a  more  delicate  one  for  very  accu- 


APPARATUS   USED   IN  ASSAYING, 


37 


rately   weighing    the    gold    and    silver    beads 
and  gold  residues. 


FIG.  15. 

Scales  for  Pulps  and  Fluxes. — Considera- 
ble latitude  can  be  allowed  in  the  choice  of 
such  scales.  Balances  can  be  procured  carry- 
ing 2,  5,  10,  20  or  30  ounces  and  upward,  and 
ranging  in  delicacy  from  -^  of  a  grain  to  i 


38  MANUAL    OF  ASSAYING. 

grain.  For  descriptions,  illustrations,  and 
prices  of  these  and  others,  see  the  lists  of 
the  various  manufacturers. 

Not  wishing  to  puzzle  the  student  too 
much,  I  specify  but  four : 

Fig.  15  represents  as  satisfactory  a  pair  as 
can  be  wanted.  It  has  a  spirit  level  and  two 
thumb-screws,  movable  scale-pans  (3^  inch 
diameter),  and  when  it  is  to  be  transported, 
all  the  parts  on  the  box  can  be  packed  in  the 
drawer.  Its  capacity  is  10  oz.  (about  311 
grammes),  and  it  is  sensible  to  -fa  of  a  grain 
(about  3^  milligrammes).  Its  cost  is  $22.00. 
(See  Becker's  list,  No.  19.)  A  glass  case  in 
which  to  keep  the  scales  is  a  good  thing  to 
have,  and  costs  $6.00. 

Troemner  makes  a  similar  balance,  capaci- 
ty 16  oz.,  sensibility  -fa  grain,  diameter  of 
pans,  4  inches,  price  $18.00.  (See  Troem- 
ner's  list,  analytical  scale  No.  2,  fig.  22.) 

A  still  cheaper  but  satisfactory  balance, 
similar  to  the  preceding,  is  likewise  furnished 
by  Troemner,  capacity  8  pz.,  sensibility  -fa 


APPARATUS    USED  IN  ASSAYING. 


39 


grain,    diameter    of    pans    3^     inches,    price 
$15.00.      It    is    represented    in    fig.  16.      The 


FIG.  16. 

objections  to  it  are  that  it  lacks  the  spirit 
level  and  adjusting  screws,  so  that  it  is  not 
always  easy  to  get  it  into  perfect  equilibrium. 

Directions  for  Setting-up  and  Testing. — 
The  various  parts  of  the  scales  shown  as  fig. 
15  come  wrapped  and  packed  in  the  drawer 
beneath.  They  should  be  carefully  un- 
wrapped, rubbed  a  little,  if  necessary,  with 
some  soft,  clean  and  dry  buck  or  chamois 
skin,  and  put  into  place  in  the  following 
order : 

A  brass  wire,  somewhat  U-shaped,  is  to  be 


4O  MANUAL   OF  ASS  A  YING. 

run  up  from  the  under  side  of  the  top  of  the 
box  stand  through  two  holes.  The  ends  of 
this  wire  pass  through  two  holes  in  the  base 
of  the  pillar  (which  is  now  standing  on  the 
box),  and  are  there  held  by  two  screws, 
shown  in  the  cut.  Next  the  swinging  needle 
(also  variously  known  as  the  index  needle, 
needle  indicator,  indicating  rod,  index  pointer 
or  pointer)  is  firmly  screwed  on  to  the  centre 
of  the  beam,  and  the  latter  placed  on  the 
knife  edges  in  the  socket  on  top  of  the  pillar. 
Upon  the  knife  edge  at  each  end  of  the 
beam  is  placed  one  of  the  little  frames  or 
stirrups  having  a  knife  edge  and  hook,  the 
latter  to  point  forward.  It  will  be  observed 
that  each  end  of  the  beam  and  each  stirrup  is 
marked  with  one  or  more  dots.  They  must, 
therefore,  be  put  together  appropriately,  that 
is,  the  stirrup  with  say  two  dots  is  to  be 
placed  on  that  end  of  the  beam  which  also 
has  two  dots,  and  so  on.  The  wire  frames 
that  support  the  scale  pans  are  now  taken, 
the  brass  piece  at  bottom  of  each  swung  out 


APPARATUS    USED  IN  ASSAYING.  41 

at  right  angles  to  the  wires,  and  the  frames 
suspended  from  the  hooks  at  end  of  beam. 
The  pans  can  then  be  placed  in  their  proper 
positions.  The  leveling  screws,  shown  at  the 
front  corners  of  the  box,  are  now  put  in  place, 
and  the  scale  is  ready  for  testing  and  after- 
ward for  work. 

To  test,  turn  the  leveling  screws  until 
the  bubble  of  air  in  the  spirit  level  is  at  rest 
in  the  centre  of  its  circular  case  ;  push  down 
the  lever  shown  in  front  of  the  graduated 
scale,  thus  allowing  the  pans  to  swing  freely, 
and  gently  vibrate  the  needle  by  directing  a 
slight  puff  of  wind  from  the  hand  upon  either 
pan.  The  needle  should  vibrate  to  the 
same  distance  on  either  side,  less  a  small 
fraction  every  time  due  to  the  decreasing 
momentum,  and  when  it  has  finally  come  to  a 
condition  of  perfect  rest  it  should  be  exactly 
in  front  of  the  central  division  of  the  gradu- 
ated ivory  scale. 

If  the  scales  are  not  in  good  order  there 
are  no  means  of  adjusting  or  correcting  (save 


42  MANUAL   OF  ASSAYING. 


such  as  the  natural  mechanical  ability  of  the 
owner  may  suggest),  and  the  best  plan  would 
be  to  exchange  them  for  a  more  perfect  pair. 
This  is  not  likely  to  be  the  case,  however, 
more  especially  since  such  scales  are  not 
required  to  be  very  delicate. 

The  directions  I  have  given  above  for  the 
setting  up  of  the  scales  shown  as  fig.  15  will 
apply,  slightly  modified,  to  any  other  and 
similar  pairs. 

Whatever  pair  be  used,  it  is  advisable  to 
take  two  large  watch  glasses,  in  diameter  a 
trifle  less  than  that  of  the  scale  pans,  and  file 
down  one  or  the  other  till  they  balance  each 
other  perfectly.  Weigh  all  charges  in  these, 
thus  avoiding  any  danger  of  corrosion  or  at- 
trition of  the  scale  pans. 

A  soft  brush  should  be  employed  to  brush 
out  the  contents  of  the  glasses. 

It  is  a  good  plan  to  always  place  the  weights 
in  one  pan  (the  right-hand  one),  and  whatever 
is  to  be  weighed  always  in  the  other. 

In  case  many  crucible  assays  are  to  be  made 


APPARATUS    USED  IN  ASSAYING.  43 

(requiring   the  weighing   of   many   fluxes),   a 

great  deal  of  wear  and  tear  of  the  balances 

described    can    be    avoided    by    substituting 

hand-scales,  which  are 

cheap  and  serviceable. 

They  are    made  with 

brass  beam, from  which 

horn    scale    pans    are 

suspended    by    means 

of    silk    threads    (fig. 

i  7).     They  can  be  se- 

FIG.  17. 

lected    irom    a    dozen 

sizes,  the  length  of  beam  ranging  between 
4  and  12  inches  (7^  or  8|  is  best  —  prices 
$2.75  and  $3.00).  Support  them  on  a  nail 
by  the  ring  at  the  top,  and  use  them  for  any 
and  all  weighings  save  those  of  the  ores.  Of 
course  no  watch  glasses  need  be  used  with 
these  scales.  Their  sensibility  is  from  -fa  to 

iro  £rain- 

Occasionally  it  becomes  necessary  to  weigh 

large  quantities  (pounds)  of  ores,  fluxes,  etc. 


44  MANUAL   OF  ASSAYING. 

Use  whatever  scales  are  easiest  obtained  ;  I 
need  not  go  into  detail  concerning  them. 

Balances  for  Weigh  ing  Gold  and  Silver  Beads. 
—  Here  likewise  is  a  range  of  choice,  and  per- 
sonal preference  comes  largely  into  play. 

When  the  assayer  intends  to  travel  consid- 
erably, the  balance  now  spoken  of  will  be  the 
most  suitable.  Length  9  to  9^  inches,  height 
Q|  inches,  width  from  3  to  4  inches.  It  packs 
into  a  light  box,  and  by  means  of  a  strong 
leathern  strap  can  be  carried  by  the  hand. 
Total  weight,  boxed,  about  4^  pounds.  With 
the  proper  weights,  this  balance  will  weigh 
Y1^  milligramme,  and  by  use  of  the  swinging 
needle  and  ivory  scale  will  indicate  -fa  milli- 
gramme. 

It  is  made  both  by  Becker  (No.  2  of  his 
list)  and  Troemner — the  prices,  with  weights 
(i  gramme  down  to  y1^  milligramme),  being 
$75  and  $65  respectively. 

When  the  balance  is  not  liable  to  be  moved 
around  very  often,  that  shown  in  fig.  18  will 
serve  nicely,  and  is  considerably  cheaper.  The 


APPARATUS    USED  IN  ASSAYING. 


45 


needle  indicates  \  of  a  milligramme,  and  each 
pan  can  bear  a  load  of  25   grammes.      Price 


FIG.  18. 


$55.00  of  either  Becker  (No.  i)  or  Troemner 
(No.  i). 

A  similar  but  larger  and   somewhat   more 

o 

delicate  balance  is  made  by  Becker  (No.  3  — 
price  $78.00).  The  needle  indicates  10  divis- 
ions on  the  scale  for  i  milligramme.  The 
greatest  objection  to  all  of  the  preceding  bal- 
ances lies  in  the  fact  that  they  have  no  grad- 
uated beam  to  carry  a  rider  to  show  the  weight 
below  10  milligrammes,  but  instead  indicate 

o 


46 


MANUAL    OF  ASSAYING. 


it  by  the  deviation  of  a  needle.     The  follow- 
ing possess  this  advantage. 


Fir..  19. 

Troemner's  No.  2.  (fig.  19  of  this  book)  is  a 
fine  balance.  The  beam  at  the  right  is  divided 
into  tenths,  each  tenth  numbered  and  corre- 
sponding to  i  milligramme,  and  furthermore 
each  tenth  is  subdivided  into  tenths,  so  that 
by  means  of  the  movable  rider  carried  by  the 
rod  (seen  in  the  upper  right  portion  of  the 
engraving),  a  button  of  -^  milligramme  can 
easily  be  weighed.  And  more  ;  since  the 
spaces  between  the  ^  milligramme  divisions 
are  appreciable,  by  placing  the  rider  half-way 


APPARATUS   USED  IN  ASSAYING. 


47 


between  any  two,  a  weight  of  ^V  °f  a 
gramme   can    be   determined.      Price    of   this 
balance,  $80.00. 


FIG.  20. 


There  is  a  still  larger  balance  (Becker  No. 
5,  Troemner  No.  3  —  price  $95.00)  which 
is  more  delicate  and  better  firiished  than  the 
preceding. 


48  MANUA  L    OF  A  SSA  YING. 

Fig.  20  is  a  good  illustration  of  Troemner's 
"  Extra  Fine  "  new  balance  (No.  5),  which  is 
noticeable  in  having  its  beam  of  aluminium. 
Has  a  double  column,  with  improved  new  ec- 
centric lift,  that  works  smoothly  and  regularly  ; 
beam  divided  on  both  ends  ;  glass  case  large 
and  roomy,  with  heavy  plate-glass  bottom  ; 
needle  indicates  forty  full  divisions  for  one 
milligramme.  Price  $175.00. 

Oertling,  of  London,  furnishes  a  most  ex- 
quisitely delicate  and  accurate  balance  (No. 
12),  represented  in  fig.  21,  which  is  regarded 
as  the  best  made.  It  is  expensive  ($175.00), 
but  where  very  delicate  work  is  required,  as 
in  weighing  the  gold  residues  from  small 
quantities  of  low-grade  ores,  it  is  indispensable. 

Notes  on  Setting-lip  the  Oertling  Balance. — 
In  mounting  this  balance,  after  the  mechan- 
ism below  the  floor  has  been  connected  with 
the  beam  supports,  and  the  standards  (or  cen- 
tral pillars)  have  been  screwed  in  position 
with  the  thumb  screw  provided,  the  beam  (with 
its  index  pointer)  is  put  in  its  place.  This 


APPARATUS    USED  IN  ASSAYING. 


49 


must  be  done  from  the  top,  and  care  should 
be  taken  that  the  pointer  is  not  bent  in  so 
doing. 


MANUAL    OF  ASS  A  YING. 


Now  adjust  the  capstan-headed  screws  on 
top  of  the  standards  in  such  a  manner  that, 
when  the  beam  is  raised  by  turning  the 
thumb  screw  in  front,  each  screw  will  touch 


the  beam  at  the  same  moment,  and  with  the 
V-shaped  support  raise  the  beam  uniformly. 
The  pointer  must  also  coincide  exactly  with 
the  zero  point  of  the  ivory  scale.  A  small 


APPARATUS    USED  IN  ASSAYING.  51 


pin  is  furnished  with  the  balance  for  turning 
the  capstan  screws. 

Now  the  pans  may  be  placed  in  position 
and  each  pan  support  adjusted  in  height  by 
means  of  its  screw  so  as  just  to  touch  the  pan, 
when  the  beam  has  been  raised  from  its  bear- 
ings. 

Fig.  22  represents  the  Ainsworth  balance, 
a  recent  but  worthy  rival  to  the  Oertling. 
In  general,  it  is  similar  to  the  latter,  but  is  so 
constructed  that  any  possible  warping  of  the 
case  will  not  affect  the  working  of  the  bal- 
ance. The  rider  attachment  is  so  arranged 
that  any  lost  motion  can  be  taken  up.  A 
magnifying  glass  is  adjusted  in  front  of  the 
needle  to  show  the  slightest  deviation.  Sen- 
sitive to  the  T^Q  part  of  a  milligramme. 
Price  $175.00. 

See  the  price  lists  of  the  manufacturers 
quoted. 

It  will  be  seen  from  an  examination  of  the 
preceding  illustrations  that  all  the  delicate 
assay  balances  are  alike  in  their  general  con- 


52  MANUAL    OF  ASSAYING. 

struction.  Each  consists  of  certain  charac- 
teristic parts,  as  herewith  described. 

First,  a  central  pillar,  or  twa  pillars,  firmly 
attached  to  the  floor  of  the  enclosing  case. 
Upon  the  top  of  the  pillar  or  pillars  is  a 
plane  bearing  a  V-shaped  crotch  lined  with 
polished  steel  or  agate  (preferably  the  latter, 
in  which  rests  the  beam  by  means  of  a  steel 
or  agate  knife  edge.  At  each  end  of  the 
beam  is  fixed  a  steel  or  agate  knife  edge, 
from  which  hangs  a  little  frame  with  a  steel 
or  agate  plane,  and  from  the  frame  is  sus- 
pended, by  a  long  and  thin  wire,  the  stirrup 
carrying  the  detachable  scale  pan. 

From  the  centre  of  the  beam  depends  a 
long,  delicate  index  needle,  which  swings  in 
front  of  a  graduated  ivory  scale. 

From  the  right-hand  side  of  the  balance 
case  of  the  Becker  and  Troemner  balances, 
and  from  both  sides  of  the  Oertling  and 
Ainsworth,  extends  inward  a  movable  rod, 
controlled  outside  the  case  by  a  milled  screw 
head.  This  rod  manipulates  a  fine  "  clothes 


APPARATUS    USED   IN  ASSAYING.  53 


pin"  of  wire  known  as  a  "  rider,"  which  can 
be  placed  on  any  point  of  the  graduated 
beam. 

By  the  employment  of  a  simple  mechanism 
the  beam  can  be  raised  from  its  agate  bear- 
ings to  avoid  unnecessary  and  wasteful  fric- 
tion or  injury  by  sudden  shocks.  This  is 
done  by  turning  the  milled  screw  head  shown 
in  front.  The  scale  pans  are  supported  when 
the  beam  is  raised  by  two  little  disks  coming 
up  from  below. 

On  the  top  of  the  index  needle  is  a  minute 
ball,  which,  by  being  either  screwed  up  or 
down,  raises  or  lowers  the  centre  of  gravity 
of  the  balance,  and  so  either  increases  or 
diminishes  its  sensitiveness. 

At  each  end  of  the  beam  of  the  Becker 
and  Troemner  balances  is  a  very  small  milled 
screw  head  which  can  be  screwed  in  or  out, 
and  by  them  the  beam  is  balanced.  On  the 
Oertling  and  Ainsworth,  instead  of  these 
screws,  a  fine  piece  of  wire  is  twisted  around 
the  little  ball  on  top  of  the  beam,  and  points 


54  MANUAL    OF  ASSAYING. 

forward,  and  by  turning  it  a  little  one  way  or 
the  other  the  same  object  is  accomplished. 

A  circular  spirit  level,  or  two  tubular  ones 
at  right  angles  to  one  another,  at  the  base 
of  the  central  pillar  or  pillars,  will  indicate 
whether  the  balance  is  or  is  not  level ;  the 
milled  screw  heads  under  the  corners  of  the 
case  are  to  do  the  regulating. 

The  whole  mechanism  of  the  balance  is 
contained  in  a  wooden  frame  with  glass  on 
the  four  sides.  Both  the  front  and  back  win- 
dows slide  up  and  down,  and  are  locked  with 
the  same  screw  or  key  which  controls  the 
beam. 

Special  Directions. — The  workmanship  of  a 
fine  balance  is  as  delicate  as  that  of  a  watch, 
consequently  the  greatest  care  should  be  used 
in  setting  it  up  and  in  handling  its  various 
parts.  Many  excellent  balances  have  been 
ruined  or  greatly  injured  by  pure  careless- 
ness, as  by  striking  the  knives,  or  by  letting 
the  beam  fall  suddenly  on  the  central  agate 
bearing,  which  will  destroy  the  delicately 


APPARATUS    USED  IN  ASSAYING,  55 

ground  knife  edges,  and,  as  a  consequence, 
the  high  sensitiveness  is  lost. 

The  agate  hangers  should  be  placed  on 
the  beam  so  that  the  marks  on  each  corre- 
spond—  that  is,  each  hanger  or  stirrup  has  a 
mark  corresponding  to  one  on  the  knife  end 
of  the  beam  to  which  it  belongs,  and,  as  the 
hangers  are  not  made  interchangeable,  cor- 
rect placing  should  be  observed. 

Care  must  also  be  used  in  handling  the 
pointer  or  needle,  that  it  is  not  bent.  Should 
it  scrape  against  the  ivory  scale  when  oscil- 
lating, lift  off  the  beam,  taking  hold  of  it  at 
the  ends,  and  lay  the  pointer  on  a  smooth, 
flat  surface  and  gently  bend  the  pointer  down- 
ward; then  replace  the  beam  and  note  any 
improvement.  If  it  still  scrapes,  remove 
beam  again  and  repeat  the  operation,  and 
continue  this  until  the  needle  will  oscillate 
perfectly  freely.  It  is  not  advisable  to  have 
the  pointer  too  far  away  from  the  ivory  scale, 
as  it  makes  it  so  much  more  difficult  to  read 
the  result. 


56  MANUAL    OF  ASSAYING. 

It  must  be  remembered  that  all  of  the  bal- 
ances described  are  very  delicate  pieces  of 
apparatus,  and  should  be  guarded  with  the 
utmost  care.  They  should  be  placed  far  from 
the  heat  of  the  furnace,  and  even  away  from 
the  rays  of  the  sun,  tending  to  unequal  ex- 
pansion and  subsequent  contraction.  Shocks 
must  be  avoided  and  even  continued  gentle 
agitation,  and  they  should  be  kept  away  from 
acid  fumes  (particularly  those  of  nitric  acid), 
and  out  of  moist  atmospheres.  By  having  a 
small  vessel  filled  with  dry  fused  calcic  chloride 
always  inside  the  case  of  the  balance,  the 
moisture  present  will  be  absorbed  by  it,  and 
thus  prevent,  in  a  measure,  the  rusting  of  the 
steel  parts  of  the  balance.  When  saturated 
replenish. 

These  balances  are  provided  with  steel 
knives  and  agate  bearings,  spirit  level  and 
set-screws.  By  means  of  the  latter  and  by 
observing  the  spirit  level,  the  balance  can  be 
placed  in  av  state  of  perfect  equilibrium,  and 
it  should  always  be  kept  in  such.  To  ascer- 


APPARATUS    USED  IN  ASSAYING.  57 

tain  whether  it  is  in  adjustment,  throw  the 
rest  down,  thus  leaving  the  pans  free,  and 
vibrate  the  needle  by  a  puff  of  wind  from 
the  hand.  The  needle  should  go  to  the  same 
distance  on  either  side,  less  a  very  small  frac- 
tion due  to  the  decreasing  momentum.  If  it 
does,  the  balance  is  in  equilibrium  ;  if  it  does 
not,  adjust  the  difference  by  means  of  a  little 
screw  at  one  end  or  the  other  of  the  beam, 
or  arrow  in  the  centre. 

To  test  its  sensibility  place  a  one-centi- 
gramme weight  in  each  pan  and  a  rider  at 
equal  distances  on  each  side  of  the  beam,  and 
see  if  in  balance.  If  not,  adjust  as  before. 
Now  move  one  of  the  riders  one  of  the  small- 
est divisions  —  the  balance  should  respond 
quickly  and  distinctly,  also  with  one-half  of 
the  smallest  divisions  (representing  with  a 
five-milligramme  rider  -^  milligramme). 

When  not  in  use,  the  rest  should  not  be 
left  down,  and  on  the  other  hand,  when  using 
the  balance,  it  should  not  be  brought  up  when 
the  needle  is  vibrating,  as  this  tends  to  throw 


58  MANUAL    OF  ASSAYING. 


the  knives  off  the  agate  bearings,  and  so  work 
injury. 

With  these  balances,  as  with  the  ore  scales, 
put  the  weights  always  in  one  pan,  the  mate- 
rial to  be  weighed  in  the  other.  Since  the 
rider  in  most  balances  is  used  on  the  beam 
at  the  right,  it  is  better  to  employ  the  right- 
hand  scale  pan  for  the  weights.  Do  not 
leave  the  weights  on  the  pan  for  too  long  a 
time. 

In  high,  dry  altitudes,  use  care  in  wiping 
the  glass  doors  of  the  balance,  as  electrical 
action  can  be  excited  which  may  affect  the 
accuracy  of  the  weighing.  Particularly  should 
any  rubbing  be  avoided  just  before  using  the 
balance. 

Cover  the  balance  when  not  in  use  with  a 
thick  woollen  cloth,  or  heavy  pasteboard  box 
lined  with  flannel  or  similar  material ;  this 
to  keep  out  dust. 

A  very  soft  and  fine  camel's  hair  brush 
may  be  employed  to  cleanse  the  scale  pans 
or  other  parts  from  dust. 


APPARATUS    USED  IN  ASSAYING.  59 

Finally,  never  use  these  balances  for  any 
other  purposes  than  for  weighing  gold  and 
silver  beads,  small  pieces  of  silver  or  gold, 
etc. 

WEIGHTS. 

The  assayer  needs  three  sets  : 

i  st.  A  set  in  the  French  or  metric  system, 
ranging  from  50  grammes  down  to  i  centi- 
gramme (10  milligrammes).  Since  they  are 
not  to  be  used  for  very  accurate  work,  but 
only  for  weighing  fluxes,  lead  buttons,  and 
other  comparatively  rough  purposes,  they 
need  not  be  very  expensive  ($5.00  to  $6.00). 

2d.  A  second  set  of  metric  weights,  to  be 
very  accurate,  their  range  from  i  gramme  to 
Y1^  milligramme,  their  use  for  weighing  gold 
and  silver  beads.  Such  a  set  is  included  in 
the  price  given  for  the  assay  balance  for  gold 
and  silver  beads  first  men- 
tioned. Separately,  they 
will  cost  $8.00  to  $10.00. 
Fig.  23  represents  a  box 
of  these  weights.  FIG.  23. 


6O  MANUAL    OF  ASSAYING. 

3d.  A  set  of  assay  ton  weights.  These 
are  important,  and  should  be  very  accurate. 
Their  range  is  from  ^  to  4  A.  T.,  and  price 
about  $6.00. 

These  weights  are  simply  invaluable  on 
account  of  their  use  requiring  no  calculations 
beyond  a  few  multiplications  or  divisions. 

But  this  assay  ton  system  of  weights  seems 
to  be  one  of  the  bug-bears  surrounding  the 
art  of  assaying  to  many  beginners,  especially 
those  advanced  in  years  and  opposed  to  prog- 
ress, and  whose  knowledge  of  weights  is  based 
entirely  upon  the  arbitrary  systems  known 
as  the  troy,  apothecaries',  and  avoirdupois. 
There  is  no  difficulty  in  understanding  it,  and 
I  think  my  explanations  will  make  the  matter 
clear  to  all. 

The  assay  ton  system  is  not  restricted  to 
any  one  system  of  weights  —  it  can  be  applied 
to  any,  be  it  in  use  in  whatever  country. 

First,  then,  to  illustrate  its  use  :  An  assayer 
weighs,  of  an  ore  to  be  tested,  \  A.  T. 
(assay  ton).  As  a  result  he  obtains  a  bead 


APPARATUS    USED  IN  ASSA  YING.  6 1 

of  silver  weighing  10  milligrammes.  If  ^ 
A.  T.  produces  10  mgrs.  (milligrammes),  i  A. 
T.  of  the  ore  will  produce  10x5=50  mgrs.  of 
silver,  and  the  assayer  reports  the  ore  as  car- 
rying 50  ounces  of  silver  to  every  ton.  If  4 
A.  T.  of  the  ore  were  used  and  a  10  mgr. 
button  obtained,  then  -^  or  2\  would  be  the 
number  of  ounces  per  ton  of  silver  that  the 
ore  would  produce.  The  simplicity  of  the 
arithmetic,  rapidity  of  calculation,  and  diffi- 
culty of  making  mistakes  are  all  apparent 
here  ;  there  remains  only  to  explain  the  con- 
nection of  the  A.  T.  with  our  ounces,  pounds, 
and  tons. 

In  this  particular  case  the  French  or  metric 
system  of  weights  is  the  one  employed  as  a 
basis  ;  but  that  is  immaterial,  as  will  be  shown 
further  along.  To  proceed :  i  ton  avoirdu- 
pois=2,ooo  pounds  avoirdupois;  i  pound 
avoirdupois=7>ooo  grains  Troy ;  therefore, 
i  ton  avoirdupois=7,ooox  2, 000=  1 4,000,000 
grains  Troy  ;  i  ounce  Tr©5z=48o  grains  Troy; 


62  MANUAL    OF  ASSAYING. 

hence  14,000,000  divided  by  480  equals  29,166 
ounces  Troy  in  i  ton  avoirdupois. 

Now  the  assay  unit,  called  the  assay  ton,  is 
(in  this  case)  a  weight  of  29.166  grammes  (a 
gramme  being  equal  to  15.4  grains  Troy),  or, 
(i  gramme  being  equivalent  to  1,000  milli- 
grammes), 29,166  milligrammes.  Hence  the 
relation  of  milligrammes  to  ounces  is  as  i  to 
i — in  other  words,  a  milligramme  corresponds 
to  an  ounce,  so  that  if  by  assay  of  i  A.  T.  of 
the  ore  we  obtain  gold  or  silver  to  the  amount 
of  4  mgrs.,  then,  without  any  calculation,  we 
know  the  ore  will  run  4  oz.  to  the  ton. 

The  above  calculation  starts  out  with  the 
short  or  American  ton  of  2,000  pounds.  The 
long  or  British  ton  weighs  2,240  pounds,  but 
we  can  use  it  in  like  manner  as  a  factor,  thus : 
7,000x2,240=15,680,000;  15,680,000  divided 
by  480  equals  32,666. 

Hence  the  unit  of  an  assay  ton  system  for 
Great  Britain  or  Canada,  based  on  the  ton  of 
2,240  pounds,  would  weigh  32.666  grammes, 
and  accordingly  as  we  took  fractions  or  multi- 


APPARATUS   USED  IN  ASSAYING.  63 

pies  of  it  in  assaying  ores,  so  would  our 
resultant  beads  of  the  precious  metals  be 
fractions  or  multiples  of  an  ounce  per  the 
long  ton. 

Those  who  may  object  to  the  metric  sys- 
tem can  still  use  the  assay  ton  system  by 
making  the  unit  a  weight  of  291.66  grains 
Troy,  or  326.66  grains  Troy.  In  actual  work, 
it  has  been  found  that  \  A.  T.  of  the  gramme 
system  equals  5.83  grammes,  equals  90.01 
grains  Troy,  is  a  good  quantity  of  ore  to 
use  in  a  scorification  assay.  An  equivalent 
amount,  or  nearly  so,  in  the  grain  assay  ton 
system  first  given,  would  be  \  A.  T.  equal  to 
97.22  grains. 

The  adoption  of  any  system  of  Assay  Ton 
weights  avoids  long  calculations  and  the  use 
of  tables.  By  employing  a  whole  number  for 
the  weight,  then  dividing  the  result  by  the 
said  number  and  multiplying  the  quotient  by 
29.166  or  32.666,  we  obtain  the  same  figures 
as  by  the  Assay  Ton  system,  but  this  necessi- 


64  MANUAL    OF  ASS  A  YING. 

tates  considerable  multiplication  or  the  use  of 
previously  prepared  tables. 

Besides  the  above  three  sets,  it  will  be 
found  desirable  to  have  a  fourth  set  of  grain 
weights,  which  may  range  between  1,000 
grains  and  y^  grain,  or  300  grains  and  -^ 
grain.  They  need  not  be  extremely  accu- 
rate. The  first  set  will  cost  $10  or  $11; 
the  second  $2.  It  is  sometimes  necessary 
to  weigh  a  bead,  button  or  other  object 
directly  in  grains,  when  these  weights  will 
be  handy. 

For  large  weighings  in  pounds,  the  proper 
weights  will  usually  be  found  to  accompany 
the  scales.* 

(See  tables  of  weights  in  appendix.) 

FURNACES. 

There  are  three  distinct  and  separate  ope- 
rations to  be  performed  in  an  assay  furnace— 

*  If  many  gold  bullion  assays  are  to  be  made,  the  assayer  will 
find  it  extremely  convenient  to  have  a  set  of  so-called  "gold 
weights."  (See  the  article  "  The  Assay  of  Gold  Bullion.") 


APPARATUS    USED   IN  ASSAYING.  65 

roasting,  crucible  fusion,  and  muffle  work  (i.e. 
scorification  and  cupellation). 

In  an  assay  laboratory  of  any  extent,  where 
many  assays  are  daily  performed,  it  will  be 
advantageous,  if  not  imperative,  to  have  a 
special  furnace  for  each  of  the  above  classes 
of  work,  but  ordinarily  the  assayer  can  man- 
age to  get  along  with  one.  It  is  requisite, 
then,  that  the  one  selected  be  adapted  to 
carry  on  all  the  aforementioned  operations. 
As  to  the  particular  kind  he  must  consult  his 
individual  preference — and  his  purse.  I  can- 
not here  describe  all  the  varieties  of  furnaces 
which  have  from  time  to  time  been  devised  ; 
all  I  can  do  is  to  speak  of  a  few  considered 
the  best. 

The  heat-supplying  medium  of  a  furnace 
may  be  any  one  of  three  kinds  of  fuel,  which 
fact,  therefore,  will  serve  to  form  a  classifica- 
tion of  the  furnaces  themselves  into  three 
divisions: 

A.  Furnaces  employing  gaseous  fuel. 

B.  Furnaces  employing  liquid  fuel. 


66  MANUAL    OF  ASSAYING. 

C.    Furnaces  employing  solid  fuel. 

Strictly  speaking,  the  heat  in  any  case  comes 
from  the  combustion  of  a  gas,  for  whether  the 
fuel  be  liquid  or  solid,  the  burning  matter  is 
either  the  liquid  transformed  into  gas,  or  it 
is  gas  driven  off  from  the  solid  fuel,  But  the 
distinctions  drawn  will  do  well  enough  for  my 
purpose. 

A.    Fitrnaces  Employing  Gaseous  Fuel. 

These  are  the  so-called  gas  furnaces,  mean- 
ing thereby  that  the  source  of  heat  is  our 
common  illuminating  gas.  But  as  this  fuel 
will  not  be  on  hand  for  the  majority  of  those 
for  whom  this  book  is  written,  they  are  re- 
spectfully invited  to  pass  over  the  following 
dozen  pages. 

The  furnaces  I  am  about  to  describe  are 
made  by  the  Buffalo  Dental  Manufacturing 
Company.  This  company  manufactures  fur- 
naces for  either  crucible  or  muffle  work,  or  both, 
some  of  which  require  a  blast,  others  only  the 
natural  pressure  of  the  gas.  The  student  is 


APPARATUS    USED  IN  ASSAYING. 


67 


referred   to   their   circulars,   also   to   Mitchell, 
pages  79  to  100. 


FIG.  24. 


68 


MANUAL    OF  ASSAYING. 


Figure  24  gives  a  very  faithful  representa- 
tion of  a  group  of  gas  furnaces  as  it  was  de- 
signed by  and  arranged  for  myself. 

Its  duty  is  to  do  roasting,  crucible  fusions, 
scorification  and  cupellation.  The  furnace  at 
the  left  is  for  roasting  sulphurets  or  other 


FIG.  25. 

ores,  for  experimentation  or  actual  work.  It 
is  what  is  known  as  a  Fletcher  No.  163  (shown 
in  section  as  fig.  25),  and  consists  of  a  fire- 
clay body  strapped  with  sheet-iron  bands,  and 
a  burner  (No.  16  Fletcher).  The  opening  at 


APPARATUS   USED  IN  ASSAYING.  69 

the  top  (protected  when  not  in  use  by  the 
cover  shown)  is  to  allow  the  heat  to  have  full 
play  upon  the  roasting-dish  placed  on  it. 
The  heat  and  flame  pass  from  the  burner 
through  the  furnace  and  out  and  up  the  chim- 
ney-pipe. The  funnel-shaped  pipe  over  the 
cover  is  to  catch  and  draw  the  fumes  up  the 
chimney.  When  the  burner  is  lighted  a  most 
powerful  draft  ensues,  carrying  all  odors  and 
fumes  at  once  away.  Both  the  pipe  and  hood 
are  provided  with  dampers,  controlled  by 
small  weights.  The  burner  is  connected  to 
the  gas-tap  by  stout  |  inch  bore  rubber  tub- 
ing. A  east-iron  tripod  supports  one  end  of 
the  furnace  and  keeps  everything  firm. 

Next  in  regular  order  (supposing  a  sul- 
phuret  ore  to  be  under  treatment)  is  the  mid- 
dle furnace,  for  crucible  fusions.  It,  likewise, 
consists  of  a  furnace  and  burner.  The  latter 
is  a  Fletcher  No.  15,  of  same  construction, 
however,  as  the  No.  16.  The  furnace  proper 
(shown  in  detail  in  fig.  26),  is  made  in  five 
parts,  the  central  section  (a  cylinder  of 


MANUAL   OF  ASSAYING. 

fire  clay),  the  bed- 
plate upon  which  it 
rests,  and  which  has 
an  opening  for  the 
flame  to  pass 
through,  the  cover 
(with  handle  attach- 
ed), and  which  also 
has  an  opening  filled 
by  a  plug,  all  of  fire' 
clay,  and  finally  a 
plumbago  lining, 
rubber  tube,  chim- 
ney connection  and 
damper,  as  with  the 
other  furnace. 

Finally,  at  the  right,  is  shown  a  furnace  for 
scorification  and  cupellation,  and  which  I 
have,  I  think  fitly,  designated  as  the  "  Moni- 
tor." Fig.  27  shows  it  enlarged  and  uncov- 
ered. In  form  it  is  almost  that  of  the  re- 
verberatory  furnace,  the  movable  bricks,  when 
in  place,  being  the  roof.  Looking  at  it  from 


FIG.  26. 


APPARATUS    USED  IN  ASSAYING.  J\ 


another  point  of  view,  it  may  be  described  as 
a  muffle  with  the  flame  as  well  as  the  heat 
inside.  Its  exterior  dimensions  are  as  fol- 
lows: 20  inches  long,  7  inches  wide  and  5^ 
inches  deep.  In  the  interior,  upon  the  bot- 


FIG.  27. 

torn,  are  four  little  wedge-shaped  bridges  of 
fire  clay,  which  are  movable,  and  upon  them 
rests  a  false  bottom  or  floor,  also  movable. 
The  latter  corresponds  to  the  muffle  bottom 
of  an  ordinary  furnace,  and  upon  it  is  done 


72  MANUAL   OF  ASSAYING. 


all  the  work.  It  is  3^  inches  wide  by  7! 
inches  long  and  \  inch  thick,  and  has  a  shoul- 
der or  bench  running  across  its  entire  width 
on  the  end  nearest  the  burner.  The  cover- 
ing bricks,  four  in  number,  are  each  7  inches 
long  by  2f  inches  wide  and  if  inches  high, 
each  with  a  slotted  bridge  for  its  convenient 
handling.  The  burner  is  the  No.  16,  Fletcher. 
Similar  connections  to  the  first-mentioned 
furnaces. 

The  3-inch  stove  pipes  of  all  three  furnaces 
are  fitted  into  one  long  horizontal  pipe,  which 
fits  snugly  into  the  chimney. 

The  bench  or  table  upon  which  rest  the 
furnaces  described,  is  made  of  pine,  well 
seasoned  and  firmly  jointed,  to  resist  as  much 
as  possible  the  warping  influence  of  heat 
and  to  support  the  weight  of  the  furnaces 
and  table  tiles.  Its  dimensions,  not  figuring 
on  the  top,  which  overlaps  i  inch  all  around, 
are :  4  feet  6  inches  long,  i  foot  7  inches  wide, 
and  2  feet  i  inch  high  plus  the  thickness  of 
the  top,  which  is  if  inches.  A  double  coat 


APPARATUS    USED  IN  ASSAYING.  73 

of  shellac  varnish  is  its  sole  ornamentation. 
To  the  sides  and  ends  of  the  table  top  are 
firmly  screwed  four  strips  of  band  iron  of  2\ 
inches  width  and  \  inch  thickness,  and  of 
such  lengths  as  to  alternately  overlap  at  the 
angles,  making  smooth  joints.  The  top  of 
this  sort  of  wall  is  f  inch  above  the  bed  of 
the  table.  Upon  the  latter  are  114  fire-clay 
tiles,  or,  rather,  clamps,  such  as  are  used  to 
join  house  tiles,  and  having  the  shape  of  the 
letter  "E"  less  the  middle  projection.  Their 
average  size  is  3^  inches  by  3  inches  across 
and  if  inches  high.  They  are  so  arranged 
on  the  table  as  to  leave  a  series  of  six  air 
tubes  or  chambers  running  its  entire  length. 
The  spaces  between  the  tiles  are  filled  with  a 
mixture  of  plaster  of  Paris  and  Venetian  red 
rubbed  up  with  water.  The  latter  color  is 
also  used  for  the  tiles  themselves,  and  some- 
what on  the  fire-clay  portions  of  the  furnaces. 
A  f-inch  bore  gas  pipe,  with  proper  taps 
and  nozzles,  is  screwed  to  the  front  of  the 
table. 


74  MANUAL   OF  ASS  A  YING. 

I  have  been  somewhat  lengthy  in  the  above 
detailed  descriptions,  but  have  done  so  for 
the  benefit  of  such  as  may  care  to  duplicate 
the  outfit. 

The  manner  of  operating  the  furnaces  is 
simple.  As  regards  the  roasting  furnace  it  is 
merely  to  shut  off  the  dampers  of  the  other 
furnaces,  turn  on  and  light  the  gas,  and  regu- 
late the  heat  to  suit  the  particular  ore.  (See 
under  Roasting.}  The  control  of  the  mix- 
ture of  gas  and  air  is  made  by  means  of  the 
milled  handle  at  the  burner. 

Next  as  to  the  crucible  furnace.  Remove 
cover,  turn  gas  on  full  at  tap,  light,  and  regu- 
late by  milled  handle.  Crucibles  that  contain 
charges  that  are  to  be  heated  gradually  can 
be  placed  in  the  furnace  as  soon  as  lighted; 
others  after  the  lapse  of  a  few  moments,  to 
allow  the  furnace  to  become  thoroughly 
heated.  Placing  the  charges  in  cold,  I  have 
made  good  fusions  of  refractory  ores  in  25 
minutes  from  time  of  lighting.  The  furnace 
will  take  crucibles  in  size  up  to  the  Battersea 


APPARATUS   USED  7 AT  ASSAYING.  75 

"  S,"  which  is  4^  inches  across  by  5  inches 
deep.  Use  no  covers. 

Finally  the  "  Monitor,"  for  which  I  may 
claim,  not  originality  (that  belonging  to  Mr. 
Thomas  Fletcher),  but  merely  applicability 
and  decided  improvements  in  the  form,  the 
original  one  being  the  roasting  furnace  al- 
ready described. 

To  manage  it,  remove  the  covering  bricks, 
open  the  clamper  and  shut  those  of  the  other 
furnaces,  turn  the  milled  handle  at  the  gas 
entrance  to  the  burner  back  so  as  to  allow 
a  full  flow  of  gas,  turn  gas  on  full  at  tap  and 
light,  and  put  back  the  bricks  into  place.  In 
from  12  to  20  minutes  the  interior  will  be  hot 
enough  for  work.  The  bricks  are  removed 
again,  the  charged  scorifiers  placed  on  the 
false  floor,  the  bricks  set. back,  and  the  excess 
of  gas  turned  off  at  the  burner.  When  the 
charges  have  melted,  slide  the  bricks  aside 
more  or  less,  and  principally  those  nearest 
the  burner,  to  admit  of  air  for  oxidation.  In 


76  MANUAL    OF  ASSAYING. 

cupellation,  the  gas  is  turned  down  more  than 
in  scorification. 

The  time  of  performing  either  scorification 
or  cupellation  (which  see)  varies  according  to 
the  nature  of  the  ore,  charge,  size  of  button, 
etc.,  but  is  about  the  same  as  that  occupied 
in  the  use  of  a  coke  furnace. 

The  consumption  of  gas  is  not  far  from  30 
cubic  feet  per  hour.  It  is  not  intended  nor 
claimed  that  this  furnace  can  take  the  place 
of  one  required  to  be  run  from  TO  to  12  hours 
per  day,  for  here,  of  course,  a  solid  fuel  will 
be  cheaper,  but  for  small  runnings  of  from  i 
to  4  hours  or  so  it  is  economical,  as  are  also 
the  others. 

For  small  laboratories,  then,  the  advantages 
of  this  furnace  are  many:  convenience  of  op- 
erating, whereby  the  assayer  sees  every  step 
and  stage  of  the  operation,  and  so  can  tell 
when  and  where  to  change  or  improve  ;  com- 
fort in  manipulation,  for  it  does  not  heat  up 
the  vicinity  of  the  furnace  and  the  room  itself 
(quite  a  desideratum  in  the  summer  time); 


APPARATUS    USED  IN  ASSAYING.  77 

perfect  control  of  the  source  of  heat,  so  that 
a  higher  or  lower  temperature,  a  reducing  or 
oxidizing  effect  may  be  produced  in  an  in- 
stant ;  entire  noiselessness,  in  which  charac- 
teristic it  is  the  superior  of  all  blast  assay 
furnaces;  saving  of  time,  which,  for  furnaces 
employing  coke,  charcoal  or  coal,  is  spent  in 
"  bedding  down,"  feeding,  breaking  coke,  etc. 
freedom  from  the  annoyances  of  dust,  ashes 
and  smoke ;  absence  of  waste ;  and,  finally, 
its  remaining  qualifications,  which  need  not 
be  dwelt  upon,  are  simplicity  of  construction, 
durability  and  portability. 

The  complete  plant,  as  illustrated,  costs 
very  close  to  $75.00. 

/>.    Furnaces  Employing  Liquid  Fuel. 

There  are  many  varieties  of  furnaces  that 
come  under  this  heading,  their  fuel  being 
refined  petroleum,  gasoline,  etc.  As  with  gas 
furnaces  proper,  some  are  intended  for  cruci- 
ble fusions,  others  for  muffle  work  ;  still  others 
are  for  both.  The  air  pressure  in  some  forms 


MANUAL    OF  ASSAYING. 


is  derived  directly  from  foot  bellows,  in  others 
from  air  compressed  by  an  air  pump. 

(Consult  the  circulars  of  the  Buffalo  com- 
pany already  mentioned  for  descriptions  of 
their  furnaces  ;  also  Mitchell,  pp.  72  to  78.) 

Fig.  28  represents  Hoskins'  Hydro-carbon 
Assay  Furnace. 


FIG.  28. 

The  apparatus  shown  in  full  above  has 
now  been  in  practical  operation  for  several 
years  in  many  parts  of  the  country,  and  is 
past  the  experimental  stage.  There  are  many 
inconveniences  and  annoyances  necessarily 
connected  with  the  use  of  coke  and  coal  fur- 
naces whereas  this  apparatus  does  away  with 
all  dust,  ashes,  constant  replenishing  of  fuel 


APPARATUS    USED  IN  ASSAYING. 


79 


and  a  large  amount  of  radiated  heat;  in  fact  it 
has  all  the  advantages  of  a  blast  gas  furnace, 
with  the  additional  advantage  that  it  may  be 
forced  to  almost  any  extent  without  the- use 
of  a  blower,  and  being  at  the  same  time  auto- 
matic. The  maximum  expense  of  running  is 
about  five  cents  per  hour,  and  in  our  large 
cities  will  not  exceed  three  cents.  Although 
there  has  been  and  is  a  prejudice  against  gaso- 
line as  a  fuel,  this  apparatus,  as  will  be  seen 
from  its  construction,  is  perfectly  safe,  and  no 
accident  can  occur  except  through  gross  care- 
lessness. 


FIG.  29. 


Fig.  29,  P  is  an  ordinary  force  pump,  at 
the  bottom  of  which,  at  A,  is* a  valve  whfch 
closes  automatically  upon  releasing  the  pres- 


8O  MANUAL  OF  ASSAYING. 

sure  from  the  pump;  C  is  a  check  valve, 
which  closes  the  inlet  to  the  tank  T  com- 
pletely; F  is  the  filling  screw  ;  V  is  the  vent 
screw,  for  letting  off  the  pressure  when 
through  ;  H  is  the  pipe  leading  from  the  tank 
to  the  burner  D  ;  E  is  the  burner  regulator, 
terminating  in  a  fine  point,  closing  the  orifice 
of  the  burner;  S  S  are  packing  boxes.  Upon 
opening  C  and  pumping  a  few  strokes  a  pres- 
sure is  created  in  the  tank  and  on  top  of  the 
fluid,  which  is  forced  through  the  tubes  of  the 
heated  burner,  vaporizing  the  gasoline,  which 
finally  issues  from  the  orifice  at  the  end  of  E 
as  a  highly  heated  gas,  and  burns  as  such  in  a 
powerful  blast.  After  once  starting,  the  heat 
of  the  flame  passing  through  the  burner  vapor- 
izes the  fluid  in  the  tubes,  and  hence  the  ap- 
paratus is  automatic ;  requires  pumping  up 
only  once  every  quarter  of  an  hour  or  half 
hour,  according  to  the  power  of  blast  desired. 
Its  action  may  be  controlled  from  the  heat  of 
an  ordinary  Bunsen  burner  to  that  required 
to  melt  cast  iron,  etc. 


APPARATUS    USED  IN  ASSAYING.  8 1 

Fig.  30  represents  the  muffle  furnace  which 
is  made  in  two  sizes,  one  taking  a  C  Battersea 
(inside  measurements,  8 
inches  long,  \\  inches 
wide,  3  inches  high),  and 
the  other  an  F  Battersea 
(inside  measurements, 
10  inches  long,  6  inches 
wide,  4  inches  high)  FIG.  30. 

muffle.  The  inlet  for  the  blast  is  opposite  and 
below  the  mouth  of  the  muffle,  and  cannot  be 
seen  in  the  cut.  In  this  muffle  everything 
can  be  done  that  can  be  done  in  the  ordinary 
coal  furnace  muffle. 

Fig.  31  represents  the  crucible  furnace  made 
in  two  sizes,  takingfromthelarge 
5  Hessian  (pinches  high,  3  inch- 
es across  top,  outside),  down. 

DIRECTIONS    FOR    USE. 

Close  E,  unscrew  F,  and  in- 
troduce from  two  quarts  to 
one  gallon  of  gasoline,  of  74° 
Beaume,  according  to  the  ca- 


MANUAL    OF  ASSA  Y1NG. 


pacity  of  the  tank.  Replace  F  and  close 
V ;  open  C  one  or  two  turns,  and  give  three 
or  four  strokes  of  pump  P,  and  close  C. 
Heat  the  burner  by  igniting  some  of  the 
fluid  in  a  suitable  vessel  placed  under  the 
burner  (an  old  scorifier  will  do  to  hold  the 
gasoline)  ;  when  hot  enough  apply  a  match 
and  open  E  gradually  until  the  action  is  more 
or  less  uniform.  If  no  spray  or  liquid  issues 
from  the  orifice,  the  burner  is  hot  enough. 
If  not  hot  enough,  burn  slowly  until  no  liquid 
or  spray  issues.  When  sufficiently  heated 
the  blast  can  be  made  of  any  intensity  desired 
by  the  use  of  the  pump  as  above.  To  stop 
its  action,  shut  the  regulator  E,  or  open  screw 
V,  or  both ;  when  not  in  use  the  vent  V 
should  invariably  be  kept  open.  The  mouth 
of  the  burner  D  should  be  two  to  three  inches 
from  the  fire  hole  of  the  furnace. 

For  high  temperature  and  muffle  work  pro- 
ceed as  follows  : 

First,  light  as  above,  and  heat  inside  of  fur- 
nace to  redness  at  least. 


APPARA  TUS  USED  IN  ASSA  YING.  83 

Second,  place  the  burner  against  the  inlet  of 
furnace. 

Third,  turn  out  the  blast  with  E  and  im- 
mediately turn  it  on  again  without  lighting  it 
(or  simply  blow  the  flame  out  of  the  burner 
tube),  when,  if  the  furnace  is  hot  enough,  the 
gas  will  ignite  inside  of  the  furnace.  The 
heat  can  be  regulated  as  in  the  first  method  of 
burning.  When-  burning  inside  of  furnace 
there  must  be  no  flame  in  the  burner  tube. 

C.  Fitrnaces  Employing  Solid  F^leL —  In 
this  class  are  found  the  best  known  furnaces, 
using  as  fuel,  wood,  charcoal,  coke,  hard  and 
soft  coal,  or  mixtures  of  them.  The  furnaces 
themselves  may  be  divided  into  two  general 
classes,  portable  and  permanent,  accordingly 
as  they  may  be  intended  to  be  moved  about 
or  remain  fixed. 

I.      PORTABLE    FURNACES. 

Very  many  forms  have  been  manufactured. 
Space  compels  me  to  reduce  the  description  to 
three  ;  the  Battersea,  Judson's  and  Brown's. 


84 


MANUAL    OF  ASS  A  YING. 


The  Battersea  furnace  is  of  fire  clay,  made 
in  sections  and  bound  with  iron  bands.      Fig. 


FIG.  32. 


32  is  a  sectional  view  of  the  muffle  furnace,  of 
which  the  following  sizes  are  obtainable  in 
this  country  : 


Height, 

Diameter, 

Sizes  of  Muffles, 

No. 

inches. 

inches. 

in  inches. 

Price. 

c 

27 

i4y2 

9 

long, 

3*J 

high, 

5^ 

wide 

$25 

oo 

D 

28^ 

i$y2 

10 

" 

4 

*  * 

6 

r 

30 

00 

E 

29^ 

i*U 

12 

•  • 

4 

*  * 

6 

" 

35 

00 

F 

30 

iiy2 

14 

" 

5 

*  * 

8 

'  ' 

40 

OO 

K 

48 

23 

15 

«' 

6 

" 

9 

" 

80 

00 

APPARATUS   USED  IN  ASSAYING. 


Judsori s  Sectional  Assay  Furnace  (patent- 
ed) is  represented  in  fig.  33.  Two  sizes  are 
specified.  Dimensions  in  inches  : 

, Muffle , 

.\'o.         High.       Wide.       Deep.       Long.       Wide.       High. 

1  36  1 8  13  12  6  4  (Battersea  J) 

2  42  22          16          15  <)  6  (Battersea  L) 


FIG.  33. 


No.    i    is   made   of    part   steel  and   part    iron 
(weight  about  300  pounds,  price  $45.00),  or  all 


86  MANUAL    OF  ASSAY  IXC. 

steel  (weight  250  pounds,  price  $52.00).  No.  2 
is  manufactured  both  entirely  of  cast  iron, 
and  part  iron  and  part  steel  (the  latter  weighs 
about  450  pounds,  price  $60.00). 

For  details  concerning  the  preceding  fur- 
naces consult  the  various  catalogues  and  cir- 
culars of  the  manufacturers. 

Brown  s  Portable  Assay  Furnace.      Fig.  34. 

-  This  furnace  consists  of  a  sheet-iron  frame 
27  inches  high  and  14  inches  square,  lined 
with  fire-brick  in  sections,  the  interior  being 
smooth  and  straight  from  top  to  bottom. 
The  cover  is  cast-iron,  and  is  ridged  to  lessen 
the  danger  o,f  cracking.  The  muffle  door  is 
cast-iron,  and  is  fitted  with  a  circular  open- 
ing, filled  with  mica,  that  the  operations  going 
on  within  the  muffle  may  be  seen  when  the 
door  is  closed.  The  draft-doors  are  also  of 
cast-iron,  and  are  provided  with  wheel  open- 
ings to  further  regulate  the  draft.  The  circu- 
lar holes  at  bottom  are  in  all  four  sides  of  the 
furnace,  and  serve  to  keep  cool  the  true  bot- 
tom of  the  furnace  upon  which  the  ashes  fall. 


APPARATUS   USED  IN  ASSAYING.  87 

The  muffle  seen  in  the  opening  rests  equally 
upon  the  fire-brick  in  front  and  in  the  rear  of 


FIG.  34. 

the  furnace,  leaving  a  space  of  \  inch  between 
the  end  of  the  muffle  and  the  brick  to  allow 
the  passage  of  fumes. 

The  grate  is  formed  of  cast-iron  bars,    10 


88  MANUAL    OF  ASS  A  YING. 

inches  long,  i  inch  square,  6  in  number,  rest- 
ing upon  a  cast-iron  frame. 

The  space  below  the  true  bottom  is  to  be 
filled  with  fire-brick  or  sand  or  other  material 
convenient. 

The  chimney  hole  is  5  inches  in  diameter, 
thus  accommodating  a  stove-pipe  of  same 
dimensions.  The  bottom  of  this  hole  is  1 7 
inches  from  the  true  bottom  of  the  furnace, 
and  8  inches  from  the  bottom  level  of  the 
muffle. 

There  is  a  handle  upon  each  side  of  the  fur- 
nace to  allow  more  convenient  handling. 

The  furnace  can  take  either  H  or  J  muffle 
of  the  Battersea  pattern, 

Size  H.          Length,  10^  in.         Width,  sl4  in-          Height,  3%  in. 
"     J.  "        12       "  "       6       "  "4       " 

but  is  better  adapted  for  size  J,  the  most  com- 
monly used  muffle.  Entire  weight  of  furnace 
boxed  is  125  pounds. 

The  above  furnace  possesses  the  following 
advantages  : 


APPARATUS    USED  IN  ASSAYING.  89 


i st.  Simplicity.  Having  no  complicated 
parts  to  get  out  of  order. 

2d.  Usefulness.  It  can  be  used  both  for 
muffle  work  and  for  crucible  operations. 

3d.  Capacity.  There  is  no  other  furnace 
manufactured  of  similar  dimensions  and  weight 
which  can  accommodate  so  large  muffles,  and 
consequently  produce  so  much  work  and  so 
rapidly. 

4th.  Durability.  Being  made  of  heavy 
sheet-iron,  it  cannot  be  broken  by  handling 
nor  injured  by  heating. 

5th.  Adaptability.  Any  fuel  may  be  em- 
ployed for  which  the  draft  of  the  chimney  is 
sufficient. 

6th.  Light  weight.  Boxed,  this  furnace 
weighs  but  125  pounds,  as  against  250  to  400 
pounds  of  other  furnaces. 

7th.  Cheapness.  This  furnace  is  from  one- 
third  to  two-thirds  cheaper  than  any  other 
furnace  that  will  do  as  good  work.  Boxed 
for  transportation,  $20.00. 

(See  advertisements  in  the  appendix.) 


90  MANUAL    OF  ASSAYING. 

II.     PERMANENT    FURNACES. 

Whenever  an  assayer  becomes  permanently 
settled  in  any  locality,  it  may  pay  him  to  erect 
a  brick  furnace,  which,  under  such  circum- 
stances, possesses  some  advantages  over  the 
so-called  portable  furnaces. 

For  descriptions  of  these,  whether  to  be 
used  for  roasting,  fusion,  scorification  and 
cupellation  work,  see  Mitchell,  pp.  57,  63,  etc. 
The  various  stamp  mills,  smelting  and  samp- 
ling works,  and  mining  corporations  scattered 
throughout  the  West,  have  usually  perma- 
nent furnaces  burning  coke,  charcoal,  soft  or 
hard  coal,  which  may  profitably  be  imitated. 

Fi£-  ^S  Sfives  a  vertical  section,  and  fig-  ?6  a 

o     <J  ^    o  o    ^ 

ground  plan  of  a  good  furnace,  the  front  view 
or  elevation  of  which  is  shown  in  the  frontis- 
piece. The  illustrations  being  to  scale  (^) 
need  but  little  explanation.  The  muffle  half 
of  the  furnace  is  at  the  right  of  each  figure, 
the  crucible  furnace  at  the  left,  both  con- 
structed of  fire  brick. 


APPARATUS    USED  IN  ASSAYING.  91 

The  lower  half  of  the  muffle  furnace  is 
anchored  with  ix^  inch  wrought  iron  bars 
and  ties,  and  the  upper  part  with  those  ixf 
inch. 


FIG.  35. 

The  muffle  appropriate  for  this  furnace  is 
the  L  Battersea,  I5x9x5f  inches.  Coke  or 
coal  may  be  the  fuel. 

The  above  very  convenient  modification  of 
Plattner's  furnace  was  constructed  for  Mr. 


g  2  MANUAL    OF  A SSA  YING. 

John  C.  Jackson,  Metropolitan  Block,  Chicago, 
and  although  erected  for  his  especial  work,  is 
yet  suited  to  the  necessities  of  almost  any 
assayer. 


FIG.   36. 

Furthermore,  many  a  peripatetic  assayer 
has  conjured  up  a  temporary  furnace  of  clay, 
adobe,  or  home-made  bricks,  using  a  tile  or 
large  crucible  fora  muffle,  to  meet  an  emergen- 
cy, and  when  its  days  of  usefulness  were  over, 
left  it  to  decay  and  ruin.  On  such  occasions, 
necessity  is  indeed  the,  mother  of  invention. 

FURNACE    TOOLS. 

Crucible  Tongs. —  For   placing   in,   and   re- 


APPARATUS    USED  IN  ASSAYING.  93 

moving  from,  the  furnace,  crucibles.  The  as- 
sayer  will  need  one  large  and  strong  pair,  of 
wrought  iron,  24  to  36  inches  long,  the  grip- 


Pics.  37  and  38. 

ping  ends  of  which  may  be  curved  or  straight, 
like  figs.  37  and  38,  or  tongs  can  be  procured 


FIGS.  39  and  40. 

of  either  one  of  the  two  forms  given  in  figs. 
39  and  40.  Either  one,  however,  of  the  two 
first  mentioned,  will  do  very  well. 


Q4  MANUAL  OF  ASSAYING. 

A  smaller  pair,  from  15  to  18  inches  in 
length,  for  lifting  small  crucibles  and  large 
scorifiers,  for  placing  lead  buttons  in  the  cu- 
pels, and  for  opening  and  shutting  the  doors 
of  the  furnace,  is  invaluable  (fig.  41). 


FIG.  41. 

A  still  smaller  pair  of   8  inches    in  length 
(fig.  42),  for  managing  the 
doors    of    the    furnace,    is 
handy,   but   not   absolutely 
necessary. 

Scorifier  Tongs. — The  correct  shape  is  here 
given  (fig.  43).      The  length   about  24  inches. 


FH;.  43. 

The  curved  arms  fit  the  bottom  of  the  scori- 
fier,  the  long  arm  extending  across  the  top. 


APPARATUS    USED   IN  ASSAYING.  95 

The  best  material  for  these  tongs  is 
steel,  and  they  should  not  possess 
too  much  spring.  Two  or  three 
sizes  should  be  procured,  to  accom- 
modate the  various  sizes  of  scorifiers. 

Fig.  44  represents  Judson's  patent 
steel  scorification  tongs,  arranged  for 
lifting  scorifiers  from  the  rear  of  a 
muffle  without  disturbing  those  in 
front. 

Fig.  45  shows  a  special  and  pecu- 
liar form  of  scorifier  tongs  required 
if  the  "  Monitor"  gas  furnace  de- 
scribed on  pp.  70-72  is  employed,  or, 
for  that  matter,  whenever  a  scorifier 
is  to  be  raised  by  a  perpendicular 
lift.  Length  about  15  inches,  great- 
est width,  3  inches,  and  can  be  made 
of  quarter-inch  wire.  FlG-  44- 


FIG.  45. 


96  MANUAL    OF  ASSAYING. 


Cupel   Tongs. — Several  forms  are  permissi- 
ble.    A  common  pattern  is  shown  in  fig.  46. 


FIG.  46. 

In  using  these  particular  tongs,  care  should 
be  taken  to  secure  a  firm  grasp  of  the  cupel, 
lest  it  slip  through  the  tongs  and  be  broken, 
and  the  bead  be  lost.  On  the  other  hand, 
too  much  pressure  may  crush  the  cupel. 

With  these  tongs  the  grip  should  be  made 
nearer  the  top  than  the  bottom  of  the  cupel, 
for  should  the  operator  happen  to  grasp  with 
it  a  cupel  below  the  latter's  centre  of  gravity 
(especially  when  the  cupel  is  soaked  with 
litharge),  it  will  probably  turn  over,  again 
giving  a  chance  for  loss  of  the  bead  of  pre- 
cious metals. 


FIG.  47. 

The    form    next    figured    (fig.    47)    is    not 
likely  to  cause  the  above  accident,  nor  quite 


APPARATUS   USED  IN  ASSAYING.  97 


FIG.  48. 

so  liable  to  crush  the  cupel,  and  fig.  48  illus- 
trates a  better  pair  than  either  of 
the  preceding. 

Fig.  49  represents  Judson's 
patent  cupel  tongs. 

Whatever  pair  of  tongs  is  used 
should  be  of  steel  or  wrought  iron, 
light  weight  with  not  too  strong 
a  spring,  length  from  18  to  24 
inches,  and  with  a  strong  guide. 

For  the  "  Monitor"  gas  furnace 
previously  mentioned,  and  as  a 
companion  tool  to  the  tongs  illus- 
trated on  page  95  (fig.  45),  the 
cupel  tongs  herewith  shown  as 
fig.  50  is  given.  The  arm  "a"  is 
straight,  "  b  "  is  curved  to  form  of 
cupel.  Length  about  1 8.  inches, 
material  quarter-inch  wire. 

For   considerable    of    my   work 


MANUAL    OF  ASSAYING. 


FIG.  50. 

I  have  used,  instead  of  tongs,  the  cupel 
shovel  (fig.  51),  and  cupel  rake  (fig.  52). 
The  curve  of  the  latter  fits  the  cupel.  By 
means  of  these  two  implements,  one  or  two 
cupels  can  be  easily  and  quickly  run  in  or  out 
of  the  muffle  without  danger  of  damage. 
They  can  be  of  light  weight  wrought  iron, 
and  about  24  inches  long.  For  carrying  a 
half  dozen  cupels  at  a  time,  a  second  shovel 
with  the 'blade  six  to  eight  inches  long  would 
be  serviceable. 


FIG.  51. 

All  the  tongs,  etc.,  just  described  (with  the 
exception,  perhaps,  of  Judson's,  which  are 
patented),  can  be  made  by  any  blacksmith,  or 
even  by  the  assayer  himself  by  exercising  a 
little  home  talent. 


APPARA  TUS    USED  IN  ASS  A  YING. 


99 


FIG.  52. 


Scarifier  or  Scarification 
Moulds,  Slag  Moulds,  or 
Pouring  Plates. — Two  forms 
are  here  presented.  Fig.  53 
is  of  cast  iron  and  has  nine 
holes;  the  same  is  furnished 
with  but  six.  Fig.  54  is  also 
of  iron,  and  has  the  advan- 
tage of  collecting  the  lead 
better  together,  and  the  dis- 
advantage of  having  but 
three  receptacles. 


ooo 
ooo 
ooo 


FIG.  53. 


FIG.  54. 


Any    hardware     merchant    can    provide    a 
very  good  substitute  for  either  of  the  above 


TOO  MANUAL    OF  ASSAYING. 


in  the  shape  of  a  so-called  "gem-plate"  gener- 
ally with  twelve  cavities. 

Similar  moulds  can  be  procured  of  heavy 
copper,  which  has  the  advantage  of  not  sud- 
denly chilling  the  slag  and  thus  causing  it  to 
retain  small  pellets  of  the  lead,  but  they  are 
quite  expensive,  and  if  the  iron  plates  are 
warmed  before  using,  they  will  serve  quite 
as  well. 

I  do  not  recommend  the  practice  of  paint- 
ing the  interiors  of  the  cups  with  ruddle  or 
chalk  washes. 

The  utility  of  scorification  moulds  is  obvi- 
ous; by  employing  them  the  time  of  cooling 
is  greatly  diminished,  and  the  scorifiers  can 
(but  they  had  better  not)  be  re-used. 

Large  moulds  for  receiving  fused  crucible 
charges  can  be  procured  (for  example  a 
plumber's  lead  pot),  but  as  mentioned  else- 
where, unless  crucibles  are  rare,  they  are 
not  necessary.  It  is  the  custom  in  some 
assay  offices  to  pour  a  crucible  fusion  into 
one  of  the  cavities  of  the  scorification  mould 


APPARATUS    USED  IN  ASSAYING.  IOI 

with   conical    cups   (fig.    54).      The  lead    but- 
ton   sinks  to   the   bottom   of  the  mould  and 
the  excess  of  slag,  fused  salt,  etc.,  runs  over 
the  top  and  into  any  convenient  receptacle. 
Muffle  Scraper. —  Shown  in  fig.  55.      Made 


FIG.   55. 

of  wrought  iron,  length  24  inches.  The  cupel 
shovel  spoken  of  can  be  used  for  conveying 
sand  or  bone  ash  into  the  muffle  whenever 
lead  has  been  spilled  upon  its  floor,  and  the 
scraper  employed  for  bringing  out  the  pasty 
mass  formed,  and  smoothing  down  the  sur- 
face of  the  floor  of  the  muffle. 

Pokers. — One    long     straight    one,     32-36 
inches,   of    f   inch   wrought    iron   (fig.   56),   a 


FIG.   56. 

short  one,  18  inches,  with  end  bent,  for 
muffle  work,  and  a  third  ordinary  poker,  for 
stirring  the  fire,  are  desirable. 


IO2  MANUAL    OF  ASSAYING. 

APPARATUS    USED    IN    THE    FURNACE. 

Muffles. — The  term  muffle  is  applied  to 
that  piece  of  apparatus  figured  here  in  vari- 
ous forms,  in  which  are  performed  the  opera- 
tions of  roasting,  scorification,  cupellation, 
etc.  Muffles  are  made  of  iron,  plumbago, 
or  a  refractory  mixture  (i.e.  sand  and  fire- 
clay), most  generally  the  latter.  They  can  be 
procured  in  the  market  in  almost  every  con- 
ceivable size  (the  price  lists  enumerating  some 
fifty),  besides  which  they  can  be  made  to  or- 
der of  any  special  dimensions. 

The  air-apertures  are  in  the  sides  in  some 
[.  57),  in   the  end  as  a  sin- 
opening  (not  shown  in  the 
cut)  in  the  form  most  favored 
FIG.  57.  in  this  country  (fig.  58). 

Still  other  muffles  are  open  entirely  at  both 
ends,  so  that  their  contents  can 
be  manipulated  as  well  from 
the    back    as    from    the  front. 
FIG.  58.  Any  muffle  can  be  easily  con- 


APPARA  TUS    USED  IN  ASSA  YING.  1 03 

verted  into  this  form  by  sawing  off  the  closed 
end. 

The  size  of  the  muffle  employed  will  be  de- 
termined by  the  size  and  make  of  the  furnace. 

In  case  the  furnace  is  so  constructed  that 
the  muffle  can  easily  be  taken  out  (and  it  is 
well  to  have  it  out  during  the  firing  up  and 
first  heating),  then  to  avoid  danger  of  crack- 
ing it  by  sudden  heat  it  is  best  to  place  it  on 
top  of  the  furnace  to  warm  it  somewhat  before 
putting  it  in  position. 

False  floors  to  the  muffle  are  obtainable, 
and  save  the  real  floor  from  injury  due  to 
spilled  lead,  etc.  They  are  made  of  same 
material  as  the  muffles. 

Crucibles. — These  vessels  are  made  of  vari- 
ous materials  :  black  lead  (graphite  or  plum- 
bago), French  clay,  Hessian  sand,  charcoal- 
lined  (i.e.  Hessian  sand  crucibles  with  a  lining 
of  charcoal  and  molasses),  quick  lime,  a  mix- 
ture of  magnesia  and  chloride  of  magnesium, 
alumina,  and  finally  those  for  very  special 
purposes,  of  porcelain,  iron,  platinum,  gold  or 


IO4 


MANUAL    OF  ASS  A  YINC. 


FIG.   59. 


silver.  It  is  but  few  of  these  varieties  that 
are  needed  for  the  assaying  of  gold,  silver, 
copper  and  lead  ores,  and  these  I  now  specify. 
The  so-called  clay  or  sand  cru- 
cibles are  the  ones  fitted  for  the 
'assaying  of  the  ores  of  the  four 
metals  named.  They  occur  in  two 
forms,  round  and  triangular  (figs. 
59  and  60),  with  covers  to  match. 
Almost  any  size  can  be  obtained 
from  some  one  of  the  manufactu- 
rers. In  giving  the  charges  for  cru- 
cible work  I  have  generally  indicated 
the  sizes  of  crucibles  needed.  The 
most  commonly  used  crucibles  will 
ranee  between  3^  and  4^  inches  in 

FIG.  60. 

height,  and  between  2 £  and  4^  inches 
across.  For  an  ordinary  crucible 
charge  of  one  assay  ton  and  fluxes, 
a  crucible  4^  inches  high  by  4^  across 
will  be  about  right. 

Fig.  6 1  shows  the  form  of  the 
French  clay  or  Beaufay  crucible  or 
"  fluxing  pot," 


FIG.  61. 


A  PPA  RA  T  US   USED  IN  A  SSA  YING.  I O  5 

For  muffle  lead  the  specially  shaped  cruci- 
bles figured  here  (fig.  62)  are  desirable.  The 
largest  size  can  also  be  used  for  fusions  of 
gold  and  silver  ores  in  muffle.  They  are  made 
in  three  sizes.  Those  furnished  by 
the  Battersea  company  are  known  as 
the ."  Colorado  "  crucibles.  Those 
manufactured  by  the  Denver  Fire 
FIG.  62.  Clay  Co.  are  known  as  5,  10  and  20 
gramme  crucibles.  The  sizes  are  as  follows  ; 
dimensions  approximate  : 

A  A,  "  Colorado  "  of  Battersea  Co.  or  5  gramme  of  Denver  Fire 
Clay  Co.,  2 14"  inches  high;  2*4"  inches  across. 

A,  "  Colorado  "  of  Battersea  Co.  or  10  gramme  of  Denver  Fire 
Clay  Co.,  3  inches  high;  2%  inches  across. 

B,  "  Colorado  "  of  Battersea  Co.  or  20  gramme  of  Denver  Fire 
Clay  Co.,  3^  inches  high;  3  inches  across. 

Roasting  Dishes. — These   are    made  of    re- 
fractory clay  or  black  lead,  of  the  form  indi- 
cated (fig.  63).      They  should  be 

quite  shallow.      They  are  used  for 
FIG.  63.  ,  f  .    . 

the    roasting    of    ores    containing 

much    antimony,    arsenic,    sulphur    and    zinc. 
They  are  furnished  in  sizes  ranging  from    2 


IO6  MANUAL   OF  ASSAYING. 

to  8  inches  in  diameter.  The  3-inch  dish  is 
suitable  for  roasting  \  A.  T.  The  5  and  6 
inch  sizes  can  be  employed  with  satisfaction 
for  open  air  roastings  of  i,  2  or  more  A.  T. 
(for  crucible  work),  in  place  of  the  frying-pan. 

Scarifiers. — These  articles  are  made  of  a 
material  similar  to  that  of  the  clay 
roasting  dishes.  Fig.  64  shows  the 
right  shape.  They  should  be  some- 
what shallow ;  in  texture  uniform,  and  free 
from  cracks  and  holes. 

They  can  be  procured  in  sizes  varying  from 
i  inch  to  5  inches  in  diameter. 

The  best  size  for  all  ordinary  scorincations 
is  the  2f  inch  (if  the  muffle  is  wide  enough 
to  admit  it).  This  size  takes  from  ^  to  \  A. 
T.  of  ore,  according  to  its  gravity.  The  2\ 
inch  is  well  adapted  for  re-scorifications,  that 
is,  for  reducing  in  size  too  large  lead  but- 
tons. It  can  also  be  employed  when  very 
little  of  the  ore  is  to  be  worked,  say  ^  A.  T. 

Have  the  2|  inch  in  large  quantity,  with 
one  half  as  many  2\  inch  and  perhaps  a  few 


APPARA  TUS    USED  IN  ASSA  YING.  1 07 

2\  inch.  For  certain  other  purposes  it  is 
advisable  to  have  on  hand  a  few  of  the  3  and 
3^  inch  sizes. 

As  the  manufactured  scorifiers  will  stand  a 
great  deal  of  rough  handling  without  injury, 
and  since  they  are  well  made  and  cheap,  it  is 
better  to  purchase  them,  rather  than  to 
attempt  their  home  manufacture  which  is  not 
a  very  easy  thing. 

Cupels. — Among  the  most  useful  articles 
the  assayer  possesses.  They  are  employed  to 
absorb  oxides  of  almost  all  the  metals  save 
those  of  gold  and  silver,  thus  leaving  these 
two  metals  behind  in  a  state  of  comparative 
purity.  Lead  is  the  metal'  whose  oxide, 
litharge,  they  absorb  in  great  quantity.  Any 
substance  which  will  absorb  these  various 
oxides  would  do,  but  for  many  reasons,  burnt 
bones  or  bone-ash  is  preferred.  Good  bone- 
ash  is  so  easily  and  cheaply  obtained  that  it 
seems  a  waste  of  time  to  more  than  indicate 
the  process  whereby  the  assayer  himself  may 
make  his  own  supply.  In  brief,  horse  or 


IO8  MANUAL    OF  ASSAYING. 

sheep  bones  are  boiled  repeatedly  in  water, 
their  organic  matter  (grease,  carbon,  etc.) 
burnt  away,  they  are  then  finely  ground, 
sifted  and  washed.  (Mitchell,  pp.  133-4.) 

Very  good  cupels  can  be  purchased  in  sev- 
eral sizes,  and  when  they  are  good,  can  be 
safely  packed  and  transported. 

The  one  chief  objection  to  purchased 
cupels  is  their  expense,  therefore  ordinarily 
it  is  cheaper  to  make  them,  to  do  which  I 
now  give  directions: 

The  bone-ash  which  can  be  obtained  in 
bulk  and  of  several  grades,  is  mixed,  say  one 
pound  at  a  time,  with  a  strong  solution  of 
pearl-ash  (or  carbonate  of  potash)  in  warm 
water,  till  the  mixture  adheres  well  together, 
though  it  must  not  be  at  all  pasty.  (The 
right  degree  of  moisture  is  hard  to  describe 
but  easy  to  acquire.)  When  a  portion  of  the 
mixture  is  squeezed  in  the  hand,  it  should 
cake  together  (somewhat  like  half-melted 
snow)  and  show  the  imprint  of  the  fingers. 
Now  sift  through  a  common  flour  sieve,  place 


APPARA  TUB    USED  IN  ASS  A  YING.  1 09 

the  cupel  ring  upon  a  block  of  wood  (having 
a  large  piece  of  brown  paper  spiead  out 
below  all),  fill  about  flush  with  the  surface 
with  the  sifted  bone-ash  and  strike  the 
plunger  into  the  ring  four  or  five  times  mod- 
erately heavily.  Turn  the  plunger  around  in 
the  ring  once  or  twice  and  push  the  cupel 
gently  out.  A  little  practice  will  soon  enable 
the  assayer  to  turn  out  perfect  cupels. 

The  moisture  remaining  in  the  cupels  can 
be  driven  out  by  placing  them  on  the  top  of 
the  furnace  after  a  day's  running,  or,  what  is 
better,  by  allowing  them  to  dry  in  the  normal 
atmosphere  of  the  room  or  by  exposure  to 
the  sunlight.  Cupels  thus  slowly  dried  are 
less  likely  to  crack  on  using. 

The  texture  of  the  cupel,  that  is,  its  degree 
of  porosity,  depending  on  the  fineness  of  the 
bone-ash  and  amount  of  compression,  is  quite 
important.  If  too  fine  bone-ash  is  used,  the 
cupel  will  crack  (or  "  check,"  as  it  is  some- 
times termed),  in  the  muffle  ;  if  too  coarse, 
the  cupel  will  absorb  silver,  causing  loss. 


I  10  MANUAL    OF  ASSA  YING. 

Therefore  a  medium  grade  had  best  be 
chosen.  The  above  two  difficulties  are  in  a 
measure  obviated  by  making  the  body  of  the 
cupel,  that  is,  the  lower  two-thirds,  of  coarse 
material,  and  the  upper  third  of  fine. 

If  the  cupel  is  too  compact,  cupellation 
proceeds  too  slowly  ;  if  too  loose  or  porous,  the 
cupellation  proceeds  too  rapidly,  causing  a  cer- 
tain absorption  of  silver  with  the  lead.  As  in 
everything  else,  experience  is  the  best  teacher. 

The  form  of  the  cupel  is  immaterial.  Fig. 
65  represents  the  one  which  I  prefer 
on  account  of  the  ease  with  which  it 
FIG.  65.  can  be  removed  from  the  mould. 

A  cupel  with  diameter  of  i^  inch  is  a  con- 
venient size. 

Annealing  Cups. — Shown  in  fig.  66.      Used 

fin   the  assay  of  gold  bullion.      Should 
be  well  made,  light  but  strong.     Vari- 
FIG.  66.    ous  sizes  can  be  obtained. 

Annealing  Plate. —  Employed  for  annealing 
a  number  of  slips  at  once,  in  the  gold  bullion 
assay.  In  size  about  6  inches  long,  2  wide 


APPARA  TUB   USED  IN  ASSA  YING.  I  I  I 

and  f  inch  thick.  May  be  made  of  an  old 
muffle  floor  rubbed  down.  Can  be  purchased 
of  either  fire  clay  or  plumbago. 

APPARATUS    OF    GLASS    AND    PORCELAIN, 

Sample  Bottles. — A  number  of  these,  of  two, 
four,  six  and  eight  ounce  capacity,  with  wide 
mouths  and  cork  stoppers,  are  desirable  for 
pulverized  samples  of  ores. 

Re-agent  Bottles.  -  -  The  dry  re-agents  are 
best  kept  in  wide-mouthed  bottles  (known  as 
"salt  mouths"),  glass-stoppered,  thus  prevent- 
ing the  admission  of  dust  and  moisture. 

Stone-ware  crocks  of  various  sizes  can  be 
employed  instead  of  the  bottles,  and  will,  of 
course,  contain  greater  quantities. 

Fruit-jars  with  threaded  necks  and  metallic 
caps  will  stand  transportation  better  than  the 
bottles,  and  tin  cans  or  wooden  boxes  will 
pack  more  closely  and  last  longer  than  either. 
Circumstances  will  alter  cases  if  the  labora- 
tory is  to  be  more  of  a  traveling  than  a  fixed 
one. 


I  12 


MANUAL    OF  ASS  A  YING. 


Whatever  receptacles  are  used,  they  should 
be  properly  labelled. 

Bottles,  of  course,  are  necessary  for  the  wet 
re-agents.  The  distilled  water  can  be  pre- 
served in  clean  demijohns  enclosed  in  wicker- 
work,  or  in  clean  stone  jugs. 

Wash  Bottle.  Fig.  67.—  To 
contain  distilled  or  pure  water. 
A  quart  is  the  best  size.  By 
blowing  in  at  the  opening  a,  a 
fine  stream  of  water  is  thrown 
out  through  6. 

Watch  Glasses.  Fig.  68.  —  • 
More  correctly  known  as  clock- 
glasses.  A  pair  is  desirable 

to  place  in  the  scale  pans  of  the 
ore  scales,  to  keep  injurious  sub- 
stances away  from  contact  ;  in  di- 
ameter they  should  be  slightly  less  than  that 
of  the  pans. 

Porcelain  Capsules  or  Criidbles.  —  For  hold- 
ing the  bead  of  gold  and  silver  while 
being  parted.  Two  sizes  are  conven- 


FIG.  67. 


FIG  68. 


FIG.  69. 


j  one 


inch  jn  diameter  across 


APPARA  TVS    USED  IN  ASSA  YING.  I  I  3 

top  by  f  inch  in  depth,  the  other  \\  inch  dia- 
meter by  ly1^  deep.  A  good  shape  is  that 
here  figured.  A  dozen  of  each  size  will  last 
some  time. 

Test  Tithes. — Used  in  qualitative  tests.  It 
is  well  to  have  some  of  four,  six  and  eight 
inches  in  length.  A  rack  to  hold  them  is  con- 
venient. Some  assayers  employ  them  for 
parting  gold  and  silver  beads. 

Parting  Flasks  (or  Boiling  Flasks).  —  A 
small  flask,  capacity  \  ounce,  of  form 
as  figured,  is  sometimes  used  for  part- 
ing gold  and  silver  beads,  instead  of 
FIG.  70.  test-tubes  or  porcelain  capsules.  At 
least  three  will  be  needed.  Round-bottomed 
flasks  are  also  frequently  used. 

Matrasses. — Flasks  of  the  shape  delineated 
in  fig.  71  and  used  for  the  parting  of 
gold  bullion,  are  generally  termed  ma- 
trasses. It  is  quite  important  for  the 
purposes  of  manipulation  that  the  neck 
Fio~7i.  of  the  flask  should  fit  snugly  into  the 
annealing  cups  employed.  Can  be  held  by  a 
wooden  clamp. 


MANUAL    OF  ASSAYING. 


Graduated  Apparatus*  —  An  accu- 
rately graduated  burette  (see  fig.  72) 
of  50  c.c.  capacity,  and  several  glass- 
stoppered  flasks  of  i  litre  capacity 
(1,000  c.c.),  500  c.c.,  250  c.c.,  100  c.c.,  50 
c.c.,  etc.,  will  be  needed  for  volumetric 
work.  They  can  be  purchased  suffi- 
ciently accurate  for  all  ordinary  de- 
mands. Some  measuring  cylinders 
(lipped),  of  10,  15,  25,  and  50  c.c.  ca- 
pacity, not  carefully  graduated,  are  very 
useful  in  measuring  solutions  for  the 
various  analyses. 

Glass  Beakers. — Will  be  needed  in 
the  copper  and 
other  analyses, 
chlorination  and  other 
tests,  etc.  They  should  be 
lipped  (fig.  73),  and  pref- 
erably of  thin  material 
to  stand  heat.  Several 
nests  may  be  wanted.  pIG.  73 


FIG.  72. 


APPARATUS    USED  IN  ASSAYING.  115 

Glass  Fimnels. — For  analyses  of 
different  kinds.  Should  be  of  an 
angle  of  60°  (fig.  74). 

Glass  Stirring  Rods. — Very  use- 
ful.     Cut  up  a  long  glass  rod  into 
various  lengths,   and    round    each         FlG-  74- 
end  by  holding  in  a  lamp  or  gas  flame  for  a 
minute  or  so. 

Flasks. — One  will  be  wanted  for  the  chlori- 
nation  assay  of  gold.  Several  sizes  can  be 
made  use  of,  for  wash-bottles,  to  retain  solu- 
tions for  any  length  of  time,  etc.  Should  be 
of  thin  glass. 

Separatory  Funnel. —  See  "Chlorination  As- 
say for  Gold,"  in  appendix. 

Casserole.  Fig.  75. —  Of 
porcelain.  Can  be  put  to 
many  uses,  as  small  evapo- 
rations, etc. 


FIG.  75- 


Pipettes.      Fig.  76. — A    10  c.c.  and  a  5  c.c. 


Fig.  76. 


will  be  required  in  the  copper  analysis.    They 


Il6  MANUAL    OF  ASSAYING. 

can  be  home-made  by  drawing  down  to  a  fine 

opening  one  end  of  a  glass  tube,  and  rounding 

the  other. 

Mortars  and  Pestles. — Small 
sizes  of  these  are  useful  in  pul- 
verizing re-agents,  etc.  Their 
material  may  be  either  glass  ("fig. 

77)  or  porcelain  ;  shape  as  represented. 

MISCELLANEOUS    APPARATUS. 

Note-books. — Indispensable.  Nothing  should 
be  left  to  the  memory,  but  everything  impor- 
tant relating  to  the  assay  of  an  ore  should  be 
down  in  black  and  white. 

The  number  of  the  ore,  its  character,  the 
charge  for  the  furnace,  conduct  in  the  fire, 
results  of  the  various  operations,  as  shown  by 
the  crucibles,  scorifiers,  cupels,  slags,  buttons, 
beads,  etc.,  and  all  calculations,  should  be 
taken  note  of. 

Gummed  Labels. — An  assortment  of  various 
shapes  and  sizes  will  be  found  extremely  con- 
venient. 


APPARATUS    USED   IN  ASSAYING.  117 

Boxes. — Of  pasteboard,  5^  inches  long,  3^ 
wide,  and  2  high,  to  be  used  for  pulverized 
samples.  Paper  boxes,  tin  boxes,  paper  bags, 
and  cloth  bags  are  also  used. 

Paper. — Sheets  of  heavy  brown  or  man  ilia 
paper  for  the  mixing  of  ore  samples  are  neces- 
sary. 

Sheets  of  black  glazed  paper  can  be  used 
instead,  but  it  is  better  to  reserve  these  for 
the  mixing  of  charges,  as  they  are  a  little  too 
delicate  for  rough  work.  Some  assayers  use 
pieces  of  sheet  rubber,  rubber  cloth  or  oil- 
cloth. 

Whatever  kind  be  employed,  see  that  it 
has  no  holes  to  allow  loss  of  sample  or  charge. 

Tissue  paper  for  wrapping  up  borax  glass 
into  pellets,  and  for  enfolding  minute  gold 
and  silver  beads  for  flattening,  will  be  needed. 
Filter-paper  is  indispensable  for  riltrations  ; 
also  valuable  for  removing  small  quantities 
of  moisture  from  the  interiors  of  the  porce- 
lain capsules  in  the  operation  of  parting. 


Il8  MANUAL    OF  ASSAYING. 

Clean  blotting-paper  will  do  for  the  latter 
purpose. 

The  filter  paper  may  be  obtained  in  sheets 
or  cut  round  of  any  size  wanted. 

Brushes. — Several  are  necessary.  First,  in 
case  the  rubbing-plate  is  employed,  a  large 
brush,  such  as  is  used  by  painters,  is  invalua- 
ble. 

For  brushing  charges  from  the  scale-pans 
or  glazed  paper,  a  medium  size  camel's  hair 
is  wanted,  and  for  brushing  the  scale-pans  of 
the  delicate  balances  a  very  fine  camel's  hair 
brush  is  needed. 

Pincers. — A  few  pairs  of  varying  sizes  are 
handy.  One  of  about  8  inches  in  length, 
strongly  made  of  wrought  iron,  a  4-inch  pair 
of  brass,  and  a  third  pair  with  limbs  running 
down  to  a  fine  point,  for  picking  up  minute 
gold  and  silver  beads,  will  suffice. 

Hammers. — While  the  assayer  can  get  along 
with  one  or  two  hammers,  it  is  better  to  be 
provided  with  four  or  five.  A  heavy  5-po'und 
sledge-hammer,  a  couple  of  smaller  ones  of 


APPARATUS    USED  IN  ASSAYING. 


about  two  pounds,  one  of  them  having  one 
sharp  edge  and  a  square  face  (fig.  78),  the 
other  with  both  faces  blunt,  a  small  hammer 
for  breaking  crucibles  and  scorifiers  and  flat- 
tening buttons,  and  a  Bounce  sharp-edged 
hammer  for  trimming  small  specimens  and 
flattening  gold  and  silver  beads,  are  very  con- 
venient. 


FIG.  78. 


A  sharp  hatchet  for  kindling-wood  and  a 
dull  one  for  breaking  coke  complete  the  cate- 
gory. 

Anvils.  —  A  miniature  blacksmith's  anvil 
(fig.  79),  weighing  i.o  pounds,  arid  properly 
mounted  on  a  block,  will  be  in  constant  de- 
mand. A  simple  yet  satisfactory  method  of 
mounting  the  anvil  has  been  of  .long-time  use 
in  my  laboratory.  An  oaken  block,  30  inches 


I2O  MANUAL   OF  ASSAYING. 


high  by  12  inches  through  in  both  the  other 
directions,  has  a  frame  of  i  inch  wood 
screwed  to  its  sides  at  the  top,  rising  one 
inch  above  the  surface.  On  the  top  of  the 
block  is  nailed  a  half  inch  thickness  of 
rubber  belting,  leaving  one-half  inch  space 
between  its  surface  and  the  upper  edge  of 
the  surrounding  frame.  The  anvil  is  screwed 


.     FIG.  79. 

down  to  a  piece  of  2-inch  oak  fitting  this 
space.  The  oaken  block  furnishes  a  firm 
support  for  the  anvil,  the  rubber  deadens  the 
sound  of  blows,  and  by  lifting  off  and  put- 
ting aside  the  anvil  and  its  bottom,  the  block 
serves  as  a  convenient  table  for  breaking  ores 
in  the  mortars.  An  illustration  of  this  is 
shown  on  p.  21  (fig.  3). 

Another   useful    form   of    block   and   anvil 


APPARATUS   USED  IN  ASSAYING. 


I  2  I 


FIG.  80. 


may  be  easily  constructed.  Obtain  a  good 
section  of  a  tree  trunk,  such  as 
butchers  use,  to  be  about  36 
inches  high  and  any  convenient 
width,  as  20  inches.  In  the  cen- 
tre excavate  a  hole  somewhat 
smaller  than  the  horn  of  the 
anvil  figured  above,  and  with 
a  wooden  mallet  or  block  of 
wood  and  a  heavy  sledge  ham- 
mer drive  the  anvil  firmly  home. 

A  flat  plate  of  steel,  if  by  ij-  inches  and 
\  inch  thick,  on  which  are  to  be  flattened  the 
gold  and  silver  beads,  is  useful. 
Ring-stand. — This  implement, 
made  of  cast-iron,  is  useful  for 
many  purposes;  to  hold  a  wire 
triangle  that  supports   the  por- 
celain capsule  used  in   parting, 
to    support    a    sand-bath,   wire- 
gauze,  etc.     Fig.  8 1   shows  one 
pattern. 

Wire  Triangle.  —  Of    twisted          FIG.  si. 


.    122 


MANUAL    OF  ASSAYING. 


FIG.  82. 


wire  .  (best    of    platinum),    in 
shape   as   figured,  for  support- 
ing capsules,  etc.      It  may  also 
be    strung    through    pieces    of 
pipe  stems. 
Sand-baths. — Any  flat  plates  of  tin  or  iron 
filled  with   sand.      Their  use  is  to  distribute 
the  heat  around  any  vessels  imbedded  in  the 
sand. 

Wire-gauze.  -  -  Three-inch  squares  of  iron 
wire  gauze  are  used  for  same  purposes  as  the 
sand-baths. 

Burners,  Lamps,  and  Stoves.  — When  gas 
can  be  procured,  the  Bunsen  burner 
(fig.  83)  is  the  best  supplier  of  heat 
for  small  purposes.  By  turning  the 
ring  at  the  bottom  so  as  to  close 
the  holes,  a  light-giving  flame  is 
produced  ;  by  leaving  the  holes 
open,  there  is  obtained  a  heating 
flame  due  to  the  more  perfect  combustion. 
A  large  alcohol  lamp  is  the  best  substitute  for 
the  Bunsen  burner. 


FIG.  83. 


APPARATUS   USED  IN  ASSAYING.  123 

Stoves  for  burning  gas,  gasoline,  kerosene, 
etc.,  etc.,  I  leave  for  individual  selection. 

Frying  Pan. — Aside  from  any  culinary  im- 
portance, this  kitchen  utensil  serves  a  useful 
end  in  receiving  melted  borax  glass,  spread- 
ing the  latter  out  that  it  may  cool  in  a  thin 
sheet. 

It  is  also  occasionally  employed  in  the 
roasting  of  sulphurets,  etc.,  on  a  compara- 
tively large  scale. 

In  either  case  coat  the  pan  with  chalk  or 
ruddle  paint. 

Blowpipe.  --  For  testing  minerals  and  for 
fusing  gold  and  silver  together.  There  are 
many  forms  of  this  important  little  instru- 
ment, but  a  plain  curved  one  is  as  satisfactory 
as  any  for  ordinary  blow-piping.  (Consult 
the  works  on  Blowpipe  Analysis.) 

Cupel  Moulds. — For  making  cupels.  These 
are  made  of  either  steel  or  brass,  but  prefera- 
bly of  the  latter,  since  they  do  not  rust  so 
quickly.  A  mould  generally  consists  of  three 
parts,  the  plunger  or  pestle,  which  is  convex 


124  MANUAL    OF  ASSAYING. 

at  the  bottom  to  form  the  concavity  of  the 
cupel,  the  ring  into  which  the  plunger  partly 
or  wholly  slips,  and  a  bottom  plate  upon  which 
the  ring  rests.  In  some  moulds  this  bottom 
plate  is  circular  and  fits  into  the  ring. 

Fig.  84  represents  a  good  form, 
which  is  of  brass,  and  is  furnished 
in  sizes  that  make  cupels  of  \\  and 
i^  inches  diameter.  It  has  no  bot- 
tom plate,  but  a  smooth  block  of 
hard  wood  will  serve  equally  well. 
The  cupel  this  mould  furnishes  has 
its  sides  at  right  angles  to  the  base 
(see  fig.  65).  One  advantage  this 
form  of  mould  possesses  is  that  by 
using  more  or  less  bone-ash,  cupels  of  vary- 
ing thicknesses  can  be  obtained  by  reason  of 
the  plunger  sliding  in  the  ring,  which  is  not 
the  case  with  all  others. 

A  special  machine  has  been  devised  for 
making  cupels,  but  I  am  not  at  all  certain  that 
it  turns  them  out  any  better  than  does  the 
common  mould,  nor  more  rapidly.  If  greater 


APPARATUS    USED   IN  ASSAYING.  125 

pressure  is  needed  than  that  given  by  the 
hammer  or  mallet,  a  second-hand  letter  press 
might  be  utilized,  by  knocking  off  the  upper 
plate  and  making  a  few  alterations. 

Shears. — For  cutting  gold  and  silver  bull- 
ion,   sheet    silver,    lead-foil,    etc.      Should    be 


FIG.  85. 

strong  and   have  a  keen  cutting  edge.      Fig. 
85  represents  a  good  form. 

Scissors  for  cutting  filter  papers,  etc.,  will 
be  wanted. 

Rolls  for  thinning  out  gold  and  silver  bull- 
ion are  more  needed  in  a  mint  than  elsewhere. 

Magnifying  Glass. — Pocket  size  very  useful. 

Magnet. — A  small  pocket  magnet  will  come 
in  play  very  often,  both  in  the  field  and  labora- 
tory. Metallic  iron,  magnetic  oxide  of  iron, 
nickel,  and  cobalt  are  attracted  by  it. 

Ingot  Moulds  for  gold,  silver,  and  lead  can 
be  obtained  in  twenty  or  more  sizes. 


126 


MANUAL    OF  ASSAYING. 


FIG.  86. 


Steel  Alphabets  and  Figures. — The  bullion 
assayer  will  need  these  for  stamping  bullion. 
They  should  comprise  the  numerals  from  o  to 
9,  an  alphabet,  and  certain  stamps  in  one 
piece,  as  "  Gold;"  "  Silver,"  "  Fine,"  "  Value," 
"  Total,"  "  No.,"  "  Oz.,"  and  "  $."  In  size  the 
above  may  vary  from  -^  inch  to  -|  inch.  Steel 
dies  with  name  of  mine,  company,  assayer, 
etc.,  can  be  procured  as  desired. 

Bullion  Punch. — Fig. 
86  shows   a  very  good 
punch    for    taking    a    sample 
from  lead  bullion. 

Cold  Chisels. — One  large  (i 
inch  diameter)  and  one  small 
one  (^  inch)  are  useful. 

Miners  Gold-washing  Pans. 
-See  <\  Pan  Test  for  Gold," 
in  appendix. 

Filter   Stands.     Fig.    87.— 
For  holding  funnels.   Wooden 
ones    are    easily   obtained    or 
made. 


FIG.  87. 


APPARATUS    USED   IN  ASSAYING.  12  J 

Biirette  Stands.  —  Any  simple,  neat,  and 
convenient  form  of  support  for  burettes  will 
do.  A  favorite  one  is  made  of  iron ;  the  clamp 
of  brass  with  cork-lined  jaws. 

Battery,  Platinum  Vessels,  etc. — See  "  Cop- 
per Analysis." 

Iron  Retorts. — They  are  used  for  distilling 


FIG.  88. 


off  the  mercury  from  an  amalgam.  Can  be 
found  in  sizes  ranging  from  \  to  24  pints. 
The  smallest  size  will  do  for  ordinary  work'. 
Fig.  88  illustrates  a  commonly  used  pattern. 

Chamois  Skin   or  any   other  fine    leather. 
—Used    in    squeezing   out   the   free   mercury 
from  an  amalgam. 


CHAPTER    II. 
RE-AGENTS  USED   IN  ASSAYING. 

UNDER  this  heading  I  purpose  to  speak  of 
those  re-agents  (or  substances  which  react), 
necessary  for  the  assaying  of  gold,  silver, 
copper  and  lead  ores.  I  shall  tell  what  they 
are,  how  they  act,  when  to  be  used  and  with 
what  object,  and,  finally,  how  to  prepare 
them  when  preparation  is  necessary. 

DRY   RE-AGENTS  FOR  ASSAYING. 

The  dry  re-agents  needed  for  the  assays 
described  in  this  book  are  seventeen  in  num- 
ber, as  follows  : 

1.  Bi-carbonate  of  soda. 

2.  Carbonate  of  potash. 

3.  Cyanide  of  potash. 

4.  Borax  glass  and  common  borax. 

5.  Flour. 

6.  Black  flux  substitute. 

7.  Argol  (or  cream  of  tartar). 


RE- AGENTS    USED  IN  ASSAYING.  I2Q 

8.  Common  salt. 

9.  Carbonate  of  ammonia. 

10.  Nitre. 

11.  Wood  charcoal. 

12.  Silica. 

13.  Lead  (sheet  and  granulated). 

14.  Litharge. 

15.  Iron  (nails  and  wire). 

1 6.  Silver. 

17.  Sulphur. 

i.  Bi-Carbonate  of  Soda  (chemical  name, 
hydro-sodic-carbonate). — This  is  the  ordinary 
commercial  bi-carbonate,  and  needs  no  prepa- 
ration, save  to  be  ground  free  from  lumps.  It 
is  employed  in  the  crucible  assays  of  gold,  sil- 
ver, copper  and  lead  ores.  Its  action  is  de- 
sulphurizing (that  is,  it  removes  the  sulphur 
from  ores  fused  with  it,  forming  sulphide  of 
soda),  and  oxidizing  (that  is,  converting  cer- 
tain metals,  as  iron,  tin  and  zinc,  which  may 
have  been  in  the  ores  treated,  from  the  metal- 
lic state  to  their  corresponding  oxides),  by 
means  of  the  carbonic  acid  it  contains.  Be- 
ing so  readily  fusible,  it  acts  as  a  wash  to 


I  30  MANUAL  OF  ASSA  Y1NG. 


rinse  down  from  the  sides  of  the  crucible  any 
matters  which  may  be  adhering  thereto. 

Finally,  it  has  a  most  important  bearing  as 
&flux,  meaning  that  it  forms  a  fusible  com- 
pound with  certain  impurities  of  the  ores,  as 
metallic  oxides,  etc. 

2.  Carbonate  of  Potash  (potassic  carbonate). 
—Ordinary  carbonate  (iwt  bi-carbonate)  of 
potash.  Since  a  mixture  of  the  alkaline  car- 
bonates (?>.,  carbonates  of  potash  and  soda), 
is  somewhat  more  fusible  than  either  alone, 
the  use  of  this  carbonate  is  advisable  in  cru- 
cible assays,  particularly  of  gold  and  silver 
ores.  It  should  be  ground  to  a  fine  powder 
and  kept  from  the  air,  as  otherwise  it  would 
rapidly  absorb  moisture.  Its  action  is  the 
same  as  that  of  the  bi-carbonate  of  soda. 

j>.  Cyanide  of  Potash  (potassic  cyanide).— 
The  cyanide  which  is  sold  in  cakes  can  be 
used,  after  being  pulverized,  or,  what  is  bet- 
ter, the  so-called  granulated  cyanide,  which  is 
fine  enough  for  all  purposes.  In  case  that  in 
form  of  -cakes  is  on  hand,  it  must  be  finely 


RE-AGENTS    USED  IN  ASSAYING.  131 

pulverized,  which  ought  to  be  done  in  the 
open  air,  using  an  iron  mortar,  the  top  of 
which  is  tied  over  and  around  with  a  towel. 
Also  it  is  well  to  breathe  through  a  wet  cloth 
wrapped  around  the  head  across  the  nostrils, 
for  the  cyanide  is  so  poisonous  that  inhaling 
the  fine  dust  even  is  a  dangerous  practice. 
Use  the  box  sieve  for  sifting.  Keep  from  the 
air,  as  this  salt  absorbs  moisture  therefrom. 

Employed  in  the  lead  assay.  Action  de- 
sulphurizing and  reducing  (that  is,  taking 
away  the  oxygen  from  metallic  oxides  and  so 
reducing  them  to  the  condition  of  metals  ;  it 
is  the  reverse  of  oxidizing). 

4.  Borax  Glass  (sodic  bi-borate).  -  -  The 
most  valuable  flux  the  assayer  possesses.  He 
employs  it  both  for  the  crucible  and  scorifica- 
tion  processes  for  gold  and  silver  ores,  and 
the  crucible  process  for  copper  and  lead  ores. 
It  has  a  neutral  action.  The  unfused  borax, 
in  powder,  is  often  used  in  the  lead  assay. 

The  ordinary  borax  of  the  shops  contains 
from  30  to  47  per  cent  of  water  of  crystalliza- 


132  MANUAL    OF  ASSAYING. 

tion,  which  must  be  gotten  rid  of  before  the 
borax  is  fit  for  use.  Borax,  on  being  strongly 
heated,  swells  very  considerably  while  losing 
this  water,  and  then  gradually  sinks  down  into 
a  clear  liquid,  which,  on  cooling,  becomes  the 
glass. 

Take  a  large  size  sand  crucible  ("S"  of 
Battersea  make)  and  carefully  coat  its  interior 
with  either  dry  chalk  or  chalk  wash.  Place 
this  in  a  hot  fire,  and  drop  in  small  pieces 
of  borax,  letting  the  swelling  subside  some- 
what after  each  successive  addition.  It  is 
well  not  to  allow  the.  crucible  to  become  more 
than  one-third  full  of  the  melted  borax,  as,  in 
spite  of  the  chalk  lining,  it  is  liable  to  attack 
the  crucible  and  run  through. 

When  thoroughly  fused,  appearing  like  wa- 
ter, pour  into  a  frying  pan  coated  with  chalk 
or  ruddle,  and  let  cool.  Powder  in  an  iron 
mortar  and  sift  through  a  4O-mesh  sieve.  That 
which  goes  through  had  best  be  reserved  for 
crucible  mixtures  ;  the  moderately  coarse  re- 
maining on  the  sieve  will  do  for  seorifications. 


RE- AGENTS    USED  IN  ASSAYING.  133 

A  strong  iron  coffee-mill  with  teeth  or  jaws 
close  together,  will  crush  borax  glass  very 
finely,  and  in  much  less  time  than  it  can  be 
done  with  mortar  and  pestle. 

An  iron  crucible  can  be  employed  in  place 
of  the  sand  one.  It  will  color  the  borax 
somewhat,  which,  however,  does  no  damage. 

5.  Flour. — Wheat  flour  is  serviceable  in  the 
lead  assay,  its  action  being  reducing.      But  it 
is  more  commonly  employed  together  with  bi- 
carbonate of  soda,  forming  what  is  known  as 

6.  Black  Flux   Substitute.— h.   mixture   of 
ten  parts  bi-carbonate  of   soda  and  three  of 
flour.      It  can  be  used  to  great  advantage  in 
the  crucible  assays  of  all  of  our  four  metals. 

7.  Argol  (crude  bi-tartrate  of  potash;  when 
pure  called  cream  of  tartar  or  hydro-potassic 
tartrate). — This    is    a  good   reducing    agent, 
and   is  much   used   in  the  lead  assay,  and   in 
crucible  charges  for  gold,   silver  and   copper 
ores. 

The  following  list  of  the  reducing  powers 
of  various  reducing  agents  will  be  found  to  be 


134  MANUAL   OF  ASSAYING. 

very  useful.  The  values  are  approximate 
only,  as  no  two  samples  of  any  one  listed  will 
reduce  to  exactly  the  same  amount,  but  for  all 
practical  assaying  they  are  sufficiently  near. 
I  have  included  only  those  substances  which 
are  procurable  in  alfnost  any  section  of  the 
country. 

TABLE     OF     REDUCING     TOWERS     OF    REDUCING 
AGENTS. 

Ipart  of  ll'iil  Reduce  Parts  of  Metallic  Lead 

Ordinary  wood  charcoal  22      to  30 

Powdered  coke  24 

"          hard  coal  25 

soft      "  22 

Wheat  flour  15 

Corn  starch  n%  to  13 

Laundry  starch  u}4  to  13 

Pulverized  white  sugar  14^2 

gum  arable  n 

Crude  argol  S/4  to    &/4 

Cream  of  tartar  4/4  to    6*4 

See  chapter  III.,  iv.,  pp.  161-2  for  methods 
of  determining  reducing  powers  of  above 
substances. 


RE-AGENTS   USED  IN  ASSAYING.  135 

8.  Common  Salt  (sodic  chloride). — Ordi- 
nary table  salt.  Very  useful  in  -every  cruci- 
ble assay.  It  serves  somewhat  as  a  protect- 
ing cover,  and  as  a  wash,  bringing  down  from 
the  sides  of  the  crucible  adhering  metals  or 
fluxes.  If  moist,  place  in  frying  pan  and 
heat  till  dry,  then  crush  free  from  lumps. 

£>.  Carbonate  of  Ammonia  (ammonic  car- 
bonate).— Of  very  little  importance,  save  to 
assist  in  the  roasting  of  certain  ores.  It  ex- 
erts a  desulphurizing  action.  To  be  employed 
as  a  fine  powder. 

10.  Nitre  or  Saltpetre  (potassic  nitrate).— 
Ordinary  saltpetre  of  commerce.  Is  a  basic 
flux  and  oxidizing  agent,  and  is  used  in  the 
crucible  assays  of  gold,  silver  and  lead  ores. 
Pulverize  finely  and  keep  dry.  Determine 
oxidizing  power  as  shown  on  page  162. 

n.  Wood  Charcoal  (carbon,  more  or  less 
impure). — Very  valuable  on  account  of  its 
reducing  and  desulphurizing  properties.  It 
exercises  the  latter  action  when  employed  in 
the  roasting  of  antimonial  and  arsenical  gold 


136  MANUAL    OF  ASSAYING. 

and  silver  ores.  Let  it  be  in  a  fine  condition, 
keep  dry,  and  determine  reducing  power  in 
same  manner  as  for  argol  or  cream  of  tartar. 
(See  page  161.)  One  part  of  ordinary 
wood  charcoal  will  reduce  from  22  to  nearly 
32  parts  of  metallic  lead  from  litharge, 
according  to  the  purity  of  the  charcoal.  In 
the  scorification  assay  of  certain  ores  (arsen- 
ical, antimonial,  etc.),  charcoal  exerts  a 
beneficial  action  in  breaking  up  the  crust 
which  sometimes  forms  on  the  surface  of  the 
charge.  A  few  pieces  of  roughly  pulverized 
charcoal  introduced  into  the  matrass  in  part- 
ing gold  bullion,  excite  local  action  and  so  pre- 
vent the  bumping  of  the  nitric  acid  solution. 

There  are  quite  a  number  of  substances  con- 
taining carbon  in  varying  proportions,  which, 
for  the  sake  of  their  reducing  action,  might 
be  used  as  substitutes  for  cream  of  tartar  and 
charcoal,  but  not  one  of  them  is  so  effective 
as  either  of  the  two  mentioned,  and  since  the 
latter  are  so  easily  obtained,  I  refrain  from 
extending  the  list  given  on  page  134. 


RE-AGENTS    USED  IN  ASSAYING.  137 

12.  Silica  (silicic  di-oxide). — This  is  a  valu- 
able acid  flux,  that  is,  it  is  to  be  used  as  a*  flux 
for  ores  which  are  basic  in  character  (as  calc 
spar,  dolomite,  barytes,  fluor  spar,  etc.),  also 
for  ores  containing  large  quantities  of  iron 
oxides  and  carbonates  and  with  little  or  no 
silica.  It  is  required  for  the  assays  of  cer- 
tain ores  of  gold  and  silver  in  both  the  cruci- 
ble and  scorification  processes,  as  will  be 
shown.  The  best  form  in  which  to  use  it  is 
as  precipitated  silica  (sold  very  cheaply), 
since  it  is  then  in  a  very  fine  state  of  division 
suitable  for  intimate  mixture  with  ores  and 
fluxes.  It  should  be  perfectly  dry. 

As  substitutes,  in  emergencies,  fine,  clean, 
dry  sand  can  be  used,  and  some  kinds  of 
glass  (which  are  silicates  of  soda  or  potash, 
with  lime,  lead,  etc.).  Lime  glass  is  to  be 
preferred,  but  on  no  account  is  lead  glass,  or 
any  containing  arsenical  compounds  or  easily 
reducible  metallic  oxides,  to  be  employed. 
Common  window  glass  and  ordinary  bottle 
glass,  broken  finely,  will  serve,  and  will  be 


138  MANUAL  OF  ASSAYING. 

found  to  be  free  from  objectionable  metallic 
ingredients. 

There  is  no  advantage  gained  in  using 
these  substitutes,  since  the  precipitated  silica 
answers  admirably,  only  it  is  well  to  know 
what  to  make  use  of,  in  case  supplies  run  out. 

/j>.  Lead. — In  thin  sheets,  called  lead-foil, 
this  metal  is  occasionally  necessary  for  cupel- 
lations,  as  described  under  the  assaying  of 
gold  and  silver,  and  in  the  gold  bullion  assay. 
It  should  be  tested  for  silver.  (See  page  160). 

In  the  granulated  form  (when  it  is  some- 
times called  test  lead)  lead  is  as  invaluable 
as  borax  glass  for  the  scorification  assay.  It 
can  be  purchased  of  varying  degrees  of  fine- 
ness and  purity,  or  it  can  be  made  from  bar 
lead  by  the  assayer  himself,  as  here  directed. 

Melt  pieces  of  the  bar  lead  in  any  conven- 
ient vessel  (odd  sizes  of  sand  crucibles,  for 
instance),  and  when  it  is  of  a  temperature 
just  hot  enough  to  char  a  splinter  of  wood, 
pour  into  a  compactly-joined  cigar  box  with- 
out a  cover,  or  a  strong  starch  box.  Imme- 


RE-AGENTS  USED  IN  ASSAYING.  139 

diately  give  a  gentle  rotary  motion  to  the 
contents  of  the  box,  till  the  lead  begins  to 
thicken,  and  emits  a  slight  creaking  noise, 
when  the  motion  is  to  be  increased  to  a  final 
vigorous  shaking  from  side  to  side.  A  min- 
ute or  two  of  this  latter,  and  the  thing  is 
done.  Sift  through  a  2O-mesh  or  an  ordinary 
flour  sieve,  and  remelt  that  which  remains  on 
the  sieve.  When  the  entire  batch  has  been 
thus  granulated,  assay  for  silver,  following 
the  directions  on  page  158. 

/^.  Litharge  (plumbic  mon-oxide,  yellow 
oxide  of  lead). -^-Employed  mainly  for  the 
crucible  assays  of  gold  and  silver  ores.  It 
should  be  dry,  and  free  from  any  considera- 
ble amount  of  red  oxide  of  lead,  as  this 
causes  oxidation  of  silver,  and  consequently 
loss.  Mitchell  says:  "  Ordinary  litharge  can 
be  easily  freed  from  this  oxide  by  fusing  it 
and  pouring  it  into  a  cold  ingot  mould,  then 
pulverizing,  and  carefully  keeping  it  from 
contact  with  air,  as  it  readily  absorbs  oxygen, 
and  if  it  be  allowed  to  cool  in  the  atmos- 


I4O  MANUAL   OF  ASSAYING. 

phere,  it  will  nearly  all  be  converted  into  the 
red  oxide." 

Litharge  can  quite  easily  be  procured  free 
from  large  quantity  of  red  oxide,  and  if  it  is 
kept  in  a  tightly-stoppered  bottle  or  tin  can 
with  closely  fitting  cover,  there  is  little  dan- 
ger of  conversion  to  this  oxide. 

It  is  used  to  furnish  metallic  lead  that 
serves  as  a  solvent  for  the  precious  metals  in 
the  ore.  When  in  the  melted  state  it  has 
the  power  of  giving  up  its  oxygen  to  almost 
all  the  metals  (save  gold,  silver  and  those  of 
the  platinum  group),  converting  them  into 
oxides,  and  since  these  are  generally  ex- 
tremely fusible,  they  go  into  the  slag.  Thus 
we  are  able  to  separate  gold  and  silver  from 
any  baser  metals  they  may  be  combined  or 
associated  with. 

Litharge  is  a  very  powerful  desulphurizing 
agent  (see  Mitchell,  pp.  181  to  187),  and  also 
serves  as  a  metallic  flux. 

It  may  safely  be  stated  that  all  litharge 
contains  silver  to  a  greater  or  less  degree. 


RE- AGENTS    USED   IN  ASSAYING.  141 

It  may  be,  and  generally  is,  in  small  quantity, 
but  it  is  absolutely  necessary  to  determine 
the  amount,  and  to  allow  for  it  in  the  calcula- 
tion of  silver  in  any  ore  tested. 

For  the  determination  of  this,  see  page  154. 

White  lead  (ceruse,  plumbic  carbonate,  or 
carbonate  of  lead),  and  sugar  of  lead  (plumbic 
acetate),  can  be  made  use  of  as  substitutes 
for  litharge,  but  they  do  not  act  quite  so  well. 

75.  Iron. — A  good  desulphurizing  agent, 
and  as  such  is  much  employed  in  the  assay  of 
galena  or  sulphide  of  lead.  Wire  of  y1^-  inch 
diameter,  and  eight-penny  nails  are  the  cor- 
rect sizes.  Iron  filings  can  sometimes  be 
used. 

16.  Silver. — Can  be  bought  as  very  thin 
foil.  It  is  quite  often  needed  in  inquartation 
(which  see).  It  should  be  tested  for  gold  by 
dissolving  -J-  gramme  in  pure  nitric  acid.  After 
the  solution  is  complete,  there  should  be  no 
black  specks  (gold),  no  matter  how  small,  in 
the  liquid.  There  is  generally  no  difficulty  in 
procuring  silver  perfectly  free  from  gold. 


142  MANUAL    OF  ASSAYING. 

77.  Sulphur. —  Ordinary  commercial  sul- 
phur. It  is  the  sulphurizing  agent.  Used  in 
Aaron's  crucible  method  to  form  mattes. 

(Oxide  of  iron  and  iron  pyrites  may  be 
wanted  for  the  assay  of  refractory  copper 
ores  —  they  need  no  especial  description.) 

WET    RE-AGENTS    FOR    ASSAYING. 

The  ivet  re-agents  necessary  in  the  assaying 
of  our  chosen  four  metals,  are  but  two  in 
number  ;  distilled  water  and  nitric  acid. 

I.  Distilled  Water. —  It  is  not  worth  the 
while  to  give  directions  for  the  preparation  of 
this  liquid  ;  it  is  simply  to  boil  water  and  con- 
dense the  steam  by  those  means  most  con- 
venient to  the  assayer.  It  can  be  purchased 
in  the  large  cities,  but  is  quite  expensive. 
Pure  rain  water  is  a  very  fair  substitute. 
The  mail?  point  in  any  case,  is  to  see  that  it 
contains  no  chlorine  (indicating  usually, 
chloride  of  sodium  or  common  salt).  Test 
the  water  for  this  element,  by  acidulating  a 
clear  sample  with  pure  nitric  acid,  and  adding  a 


RE-AGENTS  USED  IN  ASSA  YING.  143 

drop  or  two  of  nitrate  of  silver  solution  (made 
by  dissolving  one  part  of  the  dry  nitrate  of 
silver  in  twenty  parts  of  distilled  water).  The 
water  should  remain  perfectly  clear,  that  is, 
theie  should  not  be  in  it  the  slightest  cloudi- 
ness or  turbidity.  If  it  does  show  this,  reject, 
and  prepare  or  secure  a  fresh  supply. 

2.  Nitric  Acid  (\\y&ric  nitrate). — Indispens- 
able for  parting,  i.e.,  the  separation  of  silver 
and  gold  by  dissolving  out  the  former.  It  can 
be  procured  perfectly  pure,  but  should  always 
be  tested  for  chlorine,  in  same  manner  as  is 
distilled  water.  Should  it  contain  this  objec- 
tionable ingredient,  it  can  be  removed  by 
adding  one  drop  of  nitrate  of  silver  solution 
and  letting  the  acid  stand  in  the  light  till  the 
purple-black  precipitate  of  chloride  of  silver 
settles  to  the  bottom  of  the  bottle.  Then  add 
a  second  drop,  and  let  remain  undisturbed  as 
before.  Continue  these  successive  single  drop 
additions  until  finally  the  last  drop  ceases  to 
form  any  precipitate  or  milkiness  in  the  acid. 
Draw  off  the  clear  acid  and  keep  tightly  stop- 


144  MANUAL    OF  ASSAYING. 

pered.  There  are  two  reasons  why  chlorine 
should  not  be  found  in  the  nitric  acid.  First, 
it  will  tend  to  throw  down,  as  silver  chloride, 
the  silver  dissolved  ,out  of  a  bead  by  the 
nitric  acid  in  the  process  of  parting.  Secondly, 
it  indicates  the  presence  of  hydrochloric  acid, 
and  this  acid  forms  aqzia  regia  with  the  nitric 
acid,  which  could  easily  dissolve  the  very 
small  amounts  of  gold  sometimes  left  after 
parting. 

RE-AGENTS    FOR    ANALYSIS. 

The  other  re-agents,  wet  and  dry,  used  in 
the  qualitative  tests,  analyses,  and  special  pro- 
cesses, are  the  following  : 

Acetic  Acid. —  Needed  in  qualitative  tests. 
Should  be  pure.  Dilute  with  two  parts  dis- 
tilled water. 

Alcohol. —  Wanted  in  the  copper  analysis 
and  perhaps  as  fuel  for  a  lamp.  Use  either 
common  alcohol  or  wood  spirits. 

Ammonia  Water  (ammonic  hydrate,  caustic 
ammonia,  aqua  ammonia). —  If  very  strong, 


RE- AGE  NTS    USED  IN  ASSAYING.  145 

dilute   one   part   with  two   parts   of   distilled 
water. 

Bi-chromate  of  Potash  (potassic  di-chro- 
mate). — Used  in  the  volumetric  determination 
of  iron.  Should  be  procured  pure. 

Black  Oxide  of  Manganese  (manganese  di- 
oxide).— Necessary  to  aid  in  the  preparation 
of  chlorine  gas.  Does  not  need  to  be  per- 
fectly pure. 

Bromine. — Used  to  remove  manganese  from 
its  solution,  by  precipitation,  in  the  volumetric 
copper  analysis.  Agitate  some  of  the  liquid 
bromine  with  distilled  water  in  a  glass-stop- 
pered bottle,  and  use  the  resulting  aqueous 
solution  for  the  precipitation. 

Carbonate  of  Ammonium  (ammonic  carbon- 
ate, carbonate  of  ammonia). — Needed  in  the 
volumetric  copper  analysis.  Should  be  pro- 
cured chemically  pure. 

Carbonate  of  Sodium  (sodic  carbonate,  car- 
bonate of  soda). — Used  in  the  volumetric  cop- 
per and  other  analyses,  to  precipitate  iron, 
manganese,  blow-pipe  test  for  manganese,  etc. 


146  MANUAL    OF  ASSAYING. 

Should  be  pure.      Dissolve  in  ten  parts  dis- 
tilled water. 

Caustic  Potash  (potassic  hydrate). —  One 
part  of  common  stick  potash,  dissolved  in  ten 
parts  of  water. 

Caustic  Soda  (sodic  hydrate).  —  In  stick 
form.  Dissolve  in  distilled  water  —  four 
parts  —  when  wanted. 

Chloride  of  Barium  (baric  chloride,  muri- 
ate of  baryta). —  One  part  of  the  pure  salt 
dissolved  in  ten  parts  of  distilled  water. 

Chloride  of  Calcium  (calcic  chloride). — The 
dry,  fused  lumps,  used  to  keep  moisture  away 
from  fine  scales.  Need  not  be  chemically  pure. 

Citrate  of  Ammoniiim  (ammonic  citrate).— 
Dissolve  one  part  of  the  salt  in  ten  parts  of 
distilled  water. 

Citric  Acid. —  Pure,  for  volumetric  copper 
and  other  analyses  —  to  keep  iron  in  solution. 

Cyanide  of  Potassium  (potassic  cyanide, 
cyanide  or  prusside  of  potash). — Pure,  for  the 
volumetric  copper  analysis. 

Ferrocyanide  of  Potassium  (potassic  ferrocy- 


RE-AGENTS   USED  IN  ASSAYING. 


147 


anide,  yellow  prussiate  of  potash). — One  part 
of  the  pure  salt,  dissolved  in  twelve  parts  of 
distilled  water. 

Hydrochloric  Acid  (muriatic  acid). — To  be 
pure.  One  bottle  may  be  of  the  concentrated, 
a  second  of  a  mixture  of  one  part  acid  with 
four  parts  of  distilled  water. 

Hyposulphite  of  Sodium  (sodic  hyposulphite 
or  thiosulphate). — The  pure  salt  is  employed 
for  the  volumetric  determination  of  mangan- 
ese, the  chlorination  test  for  silver,  and  as  a 
precipitant  for  copper  in  the  volumetric 
analyses  of  the  ores  of  this  metal. 

Iodide  of  Potassium  (potassic  iodide,  iodide 
of  potash). — Wanted  in  the  volumetric  deter- 
mination of  manganese  and  as  a  test  re-agent 
for  lead.  When  used  for  the  latter  purpose,  it 
may  be  either  in  the  solid  form,  or  in  solution 
in  water  —  one  part  in  ten. 

Lime  Water  (calcic  hydroxide). —  Place  a 
very  little  slaked  lime  in  a  bottle  ;  fill  with 
water  and  shake.  Keep  tightly  corked,  and, 
when  wanted,  draw  off  the  clear  liquid  with- 
out disturbing  the  sediment. 


148  MANUAL    OF  ASSAYING. 

Mercuric  Chloride  (corrosive  sublimate).— 
Needed  only  for  the  volumetric  determination 
of  iron,  which  see. 

Metallic  Copper. —  Wire  for  battery  pur- 
poses, sheet  for  amalgamation  test  in  panning, 
and  some  pure  to  form  test  solutions  in  the 
volumetric  copper  analysis,  will  be  needed. 

Metallic  Iron. — Pure,  to  precipitate  copper 
from  its  solution,  in  the  volumetric  analysis 
of  the  latter  metal. 

Metallic  Mercury  (quicksilver). — Some  that 
is  impure  can  be  employed  to  amalgamate  the 
zinc  plates  of  a  battery,  and  some  free  from 
gold  and  silver  will  be  wanted  in  the  various 
amalgamation  tests. 

Metallic  Zinc. — In  plates,  forming  a  part  of 
a  battery.  As  a  re-agent,  zinc  in  pencils,  or 
granulated,  will  be  needed  pure. 

Nitrate  of  Silver  (argentic  nitrate,  lunar 
caustic). —  See  testing  of  distilled  water  for 
chlorine. 

Nitric  Acid. — A  bottle  of  pure  and  concen- 
trated acid,  and  one  of  the  common  commer- 


RE- AGENTS    USED  IN  ASSAYING.  149 

cial  (concentrated)  for  battery,  should  be  on 
hand. 

Stannous  Chloride  (proto-chloride  of  tin, 
"tin  salts"). —  For  the  volumetric  determina- 
tion of  iron. 

Sulphate  of  Iron  (ferrous  sulphate,  green 
vitriol,  copperas). —  In  solution  in  water  (of 
no  particular  strength)  it  is  used  to  precipi- 
tate gold  from  its  solution  as  a  chloride,  after 
the  chlorination  assay. 

Sulphate  of  Magnesiiim  (magnesic  sulphate, 
sulphate  of  magnesia,  "  Epsom  salts  "). —  In  a 
pure  state,  to  precipitate  arseniates  in  the  volu- 
metric copper  analysis,  as  a  test  re-agent  for 
phosphates,  etc. 

Sulphide  of  Iron  (ferrous  sulphide,  sulphuret 
of  iron). —  See  next  paragraph  but  one.  Can 
be  purchased,  or  made  by  holding  roll  sulphur 
against  a  bar  of  red-hot  iron. 

Sulphocyanide  of  Potassium  (potassic  sul- 
phocyanide). — One  part  of  the  pure  salt  dis- 
solved in  ten  parts  of  distilled  water. 

Sulphuretted  Hydrogen    Water  (hydrogen 


I5O  MANUAL   OF  ASSAYING. 

sulphide  gas  dissolved  in  water). — Very  use- 
ful in  qualitative  analysis.  To  generate  it,  fit 
together  a  simple  piece  of  apparatus  similar 
to  fig.  89.  The  larger  bottle,  which  may  be 
of  any  capacity  above  six  ounces,  is  provided 
with  a  doubly-perforated  cork,  through  one 
hole  of  which  passes  a  straight  glass  tube  to 
nearly  the  bottom  of  the  bottle,  and  terminat- 
ing in  a  funnel.  Through  the  other  hole  a 
second  tube  passes  a  little  way  into  the  larger 
bottle,  and  bending  twice  at  right  angles,  goes 
through  the  cork  of  the  smaller  bottle  to 
nearly  its  bottom.  A  third  tube  leaves  this 
smaller  bottle  and  connects  by  a  bit  of  rub- 
ber tubing  with  a  fourth  tube  dipping  into 
the  receiving  bottle  containing  distilled  water. 
Place  an  ounce  or  two  of  sulphide  of  iron 
broken  in  small  pieces  in  the  bottom  of  the 
large  bottle  and  fill  half  way  up  with  ordi- 
nary water.  The  small  bottle  is  to  be  half- 
filled  with  distilled  water  to  wash  the  gas. 
Pour  some  common  sulphuric  acid  into  the 
funnel-tube,  when  the  gas  will  at  once  be 


RE-AGENTS    USED  IN  ASSAYING,  151 

given  off.  To  ascertain  when  the  water  in 
the  re-agent  bottle  is  saturated,  hold  the 
thumb  tightly  over  its  mouth,  and  shake.  On 
releasing  the  pressure  a  little  the  thumb  will 
be  held  down  if  the  water  is  not  saturated, 
but  will  be  forced  up,  if  the  contrary  is  true. 
A  little  glycerine  put  in  the  re-agent  bottle 
will  help  to  retain  the  gas  in  solution. 


FIG.  89. 

Sulphuric  Acid(v\\  of  vitriol). — A  bottle  of 
pure  and  another  of  common,  both  concen- 
trated. If  dilute  acid  is  wanted,  mix,  in  a 
beaker,  one  part  of  the  acid  with  five  of  dis- 
tilled water. 

Tartaric    Acid. —  Used     to     retain     iron, 


152  MANUAL    OF  ASSAYING. 

alumina,  etc.,  in  solution,  in  the  volumetric 
copper  analysis  and  in  qualitative  analyses. 
The  pure  salt  can  easily  be  procured. 

MISCELLANEOUS. 

Bone-ash. — For  making  cupels,  which  see. 
It  is  best  to  use  a  good  quality. 

Chalk  and  Chalk  Wash. —  Ordinary  chalk, 
to  be  used  dry,  and  the  same  finely  ground 
and  rubbed  up  with  water,  for  coating  cru- 
cibles, etc. 

Clay  Lute. —  Fire-clay  and  sand,  with  solu- 
tion of  common  borax  in  water  to  bind  them 
together.  Horse  and  cow-hair  may  also  be 
mixed  with  them. 

Riiddle  (ferric  sesqui-oxide,  red  oxide  of 
iron,  hematite). — A  lump  for  marking  cupels 
and  scorifiers,  and  a  paint  (prepared  by  put- 
ting an  ounce  or  two  of  the  fine  powder  with 
water  in  a  bottle,  and  shaking)  for  marking 
crucibles,  coating  frying-pan,  etc.,  are  wanted. 


CHAPTER  III. 

TESTING  OF  RE-AGENTS. 

* 

BEFORE  proceeding  to  make  the  regular 
assays,  the  student  will  find  it  expedient  to 
examine  his  re-agents,  either  to  ascertain  the 
presence  or  absence  of  silver  (and  in  the  for- 
mer case,  to  determine  its  quantity),  or  to 
learn  their  various  strengths,  as  shown  in 
their  reducing  or  oxidizing  powers. 

The  following  five  divisions  include  all  the 
requisite  tests  of  re-agents  : 

I.    Testing  of  Litharge  for  Silver. 
II.    Testing  of  Granulated   Lead  for  Sil- 
ver. 

III.  Testing  of  Sheet  Lead  for  Silver. 

IV.  Determination  of  the  Reducing  Pow- 

ers of  Reducing  Agents. 
V.    Determination  of  the  Oxidizing  Pow- 
er of  Nitre  (Nitrate  of  Potash). 
153 


154  MANUAL    OF  ASSAYING. 

I.     TESTING    OF    LITHARGE    FOR    SILVER. 

As  stated  in  the  chapter  on  re-agents, 
almost  all  litharge  contains  silver,  generally 
as  a  small  amount.  However  minute  this 
may  be,  we  must  know  exactly  what  it  is,  and 
allow  for  it  in  calculating  the  value  of  an  ore. 

This  we  do  by  the  crucible  process,  in  the 
same  manner  as  we  should  run  an  ore.  (See 
Part  II,  Chapter  I.) 

Mix  very  thoroiighly  the  particular  lot  of 
litharge  to  be  examined,  and  sample  as  usual. 

Make  the  charge 

* Assay  ton  [Gramme  Grain 

weights,  weights.  weights. 

Bi-carb.  soda Vz  A.  T 15     grammes..  240  grains  =  ya  oz. 

Carb.  potash %     "     jVz         "        .-  120      "      =54" 

Litharge i}4     ll     45                      ••  720              =i/4  " 

Charcoal,   [     Any     "]        V2  gramme —  ^gramme...  7*4   u 

Flour,        -j  one    of  j-     i           "       —  i                    ...  15 

Argol,         (    these,    j      2     grammes...  2      grammes..  30       " 
Salt  cover. 

Any  one  of  the  above  charges  will  produce 
a  lead  button  of  from  1 5  to  20  grammes  ( 1 3 1  to 
308  grains). 

Mix  everything  well,  and  brush  into  an  "  S  " 

*  See  Chapter  I,  pp.  60-4,  for  full  explanation  of  these  weights. 


TESTING   OF  RE-AGENTS.  155 

Battersea  crucible  or  its  equivalent  (4f  inches 
by  4^  wide). 

Have  the  fire  quite  hot,  and  heat  crucible 
till  contents  are  in  quiet  fusion,  which  will  be 
in  from  twenty-five  to  thirty-five  minutes. 
Take  out,  let  cool,  break,  and  hammer  button 
into  shape. 

If  the  button  is  too  large  for  any  cupel,  re- 
duce by  scorifying,  then  cupel.  (See  "  Scori- 
fication  and  Cupellation,"  Part  II,  Chapter  I.) 

Weigh  the  resulting  silver  button,  and  de- 
duct its  weight  from  the  gold  and  silver  bead 
obtained  from  any  crucible  assay  where  the 
same  quantity  of  litharge  has  been  employed. 
If  more  or  less  than  i^  A.  T.  (or  its  equiva- 
lent in  grammes  or  grains)  is  used,  calculate 
and  deduct  accordingly. 

For  example,  one  lot  of  litharge  I  have 
tested  carried  0.75  (J)  of  a  milligramme  for 
the  \\  A.  T.,  which  amount  was  made  the 
factor  for  that  particular  lot. 

The  above  amount,  equivalent  to  \  ounce 
per  ton  of  2,000  pounds,  is  of  course  very 


156  MANUAL   OF  ASSAYING. 

small,  and,  in  the  calculation  of  the  value  of 
an  ore  running  say  100  oz.  and  upward,  need 
not  be  deducted  from  the  weight  of  the  silver 
bead,  since  the  loss  of  silver  by  absorption 
and  volatilization  from  such  a  bead  while 
cupelling,  would  more  than  counterbalance  it. 
But  it  is  very  important  that  it  should  be 
deducted  in  the  case  of  a  poor  ore,  and 
especially  when  there  is  a  question  as  to  the 
presence  or  absence  of  silver  in  any  ore. 

For  the  sake  of  practice,  it  will  be  well  for 
the  student  to  perform  this  crucible  assay  of 
litharge  three  or  four  times. 

Many  assayers,  and  particularly  those  newly 
entered  into  the  profession,  continually  try  to 
obtain  litharge  (and  for  that  matter,  granu- 
lated lead)  free  from  silver,  meaning  that  it 
shall  contain  absolutely  no  silver.  But,  in  the 
first  place,  they  cannot  procure  it,  and,  in  the 
second  place,  if  they  could,  there  would  be 
nothing  gained,  in  my  opinion,  by  using  such, 
as  I  will  endeavor  to  show. 

First,  in  assaying  ores  which  might  be  rich 


TESTING   OF  RE-AGENTS.  157 


in  either  gold  or  silver,  it  would  make  no  dif- 
ference whether  the  litharge  employed  con- 
tained absolutely  no  silver,  or  the  small 
amount  it  usually  carries,  for  in  the  latter  case 
its  weight  would  not  be  deducted  from  that 
of  the  button  for  reasons  just  given.  Sec- 
ondly, in  ores  very  low  in  gold,  it  becomes 
very  difficult,  and  sometimes  impossible,  to 
find  the  minute  speck  of  gold  left  from  the 
assay  (particularly  as  the  result  of  a  scorifica- 
tion  assay),  even  with  the  aid  of  the  magnify- 
ing glass  ;  but  when  the  litharge  does  contain 
a  little  silver,  the  latter  not  only  leaves  itself 
and  the  gold  together  in  a  visible  and  tangible 
form  on  the  cupel,  but  it  also  serves  to  collect 
the  gold  during  the  process  of  crucible  fusion, 
and  retains  it  always  thereafter.  Thirdly,  a 
small  but  known  amount  of  silver  in  litharge, 
tests  the  assayer,  his  methods  and  practice, 
the  litharge  itself  and  some  of  the  ores  worked 
upon,  for  he  ought  to  get  the  constant  figure 
of  the  silver  in  the  litharge  when  testing  the 


158  MANUAL    OF  ASSAYING. 


many  worthless  ores  he  is  bound  to  examine 
in  the  course  of  his  work. 

II.     TESTING  OF  GRANULATED  LEAD    FOR   SILVER. 

As  in  the  case  of  litharge,  all  granulated 
lead  must  have  its  amount  of  silver  deter- 
mined, which  is  done  by  the  scorification 
process. 

Mix  and  sample  as  usual.  Rub  the  interior 
of  the  scorifier  with  a  little  fine  silica  before 
pouring  into  it  any  of  the  lead  ;  it  will  serve 
to  protect  the  scorifier  from  corrosion  by  the 
molten  lead.  Weigh  very  carefully  2  A.  T., 
60  grammes  or  960  grains  (2  oz.),  of  the  lead, 
and  pour  into  a  2f  inch  scorifier,  and  deposit 
on  the  top  a  piece  of  borax  glass  about  the 
size  of  the  head  of  a  pin. 

Scorify  and  cupel  as  shown  in  the  next 
chapter,  and  weigh  resulting  bead.  The 
weight  of  the  silver  bead,  divided  by  two,  will 
give  the  number  of  milligrammes  or  fractions, 
that  one  assay  ton  (30  grammes,  480  grains, 
or  i  ounce)  of  the  lead  contains,  which  I 


TESTING   OF  RE-AGENTS.  159 

have  found   to  vary  from  T3¥  milligramme  to 
1.2  milligrammes. 

Make  a  table  of  the  amounts  of  silver  con- 
tained in  fractions  and  multiples  of  one  assay 
ton,  and  post  it  in  some  convenient  place  for 
reference.  I  give  an  example  of  one  particu- 
lar lot  : 

0.50  A.  T.  contains  0.40  milligramme  silver. 
i. oo      "  "        0.80 

1.50      "  "         1.20 

2.00      "  "         1.60 

If  other  weights  of  lead  are  used,  calculate 
accordingly. 

Deduct  silver,  in  proportion  due  to  the 
amount  of  lead  used,  from  beads  coming  from 
ores  ranging  less  than  100  ounces;  above  that 
disregard  it,  as  with  litharge.  As  with  litharge, 
make  several  runnings  of  the  lot  of  lead. 

The  reasons  given  for  desiring  a  litharge 
with  some  little  amount  of  silver  present  are 
almost  equally  applicable  to  granulated  lead. 


l6o  MANUAL   OF  ASSAYING. 

III.     TESTING  OF  SHEET  LEAD  FOR  SILVER. 

Sheet  lead  can  generally  be  purchased  re- 
markably free  from  silver,  and  as  it  is  seldom 
that  a  piece  of  more  than  ten  or  twelve 
grammes  (120  to  150  grains)  in  weight  is  re- 
quired, the  quantity  of  silver  such  a  piece  will 
contain  will  be  exceedingly  small.  Moreover, 
its  chief  use  being  to  enwrap  gold  and  silver 
beads  for  recupellation,  this  amount  of  added 
silver  is  too  minute  to  counterbalance  the  loss 
of  silver  by  volatilization  and  absorption. 
Sheet  lead  is  sometimes  employed  to  aid  in 
cupelling  gold  beads  that  have  been  in- 
quarted,  and  here  a  loss  or  addition  of  silver 
is  not  important. 

But  should  the  lead-foil  be  suspected  of 
carrying  any  quantity  of  silver,  its  exact 
amount  can  be  determined  by  cutting  off  from 
various  parts  of  the  foil,  and  in  small  shreds, 
two  or  four  assay  tons  (60  or  120  grammes, 
2  or  4  ounces),  which  are  to  be  scorified  and 
cupelled  as  usual. 


TESTING   OF  RE-AGENTS.  l6l 


IV.    DETERMINATION  OF    THE    REDUCING    POWERS 
OF    REDUCING    AGENTS. 

/.  Argol  (p.  133). — Weigh  out  the  follow- 
ing charge : 

Bi-carbonate  of  soda. .  15  grammes,  240  grains  (  ^-oz.) 
Carbonate  of  potash..    7^        "          120       "       (  \  "  ) 

Litharge 45  720       "       (\\  "  ) 

Argol 2  30       " 

Salt  cover. 

Put  into  a  small  crucible  (size  "  V  "  of  Bat- 
tersea),  place  in  a  hot  fire,  cover,  remove 
when  thoroughly  fused,  cool,  detach  button 
from  slag,  weigh,  following  the  directions 
given  for  the  crucible  assays  of  gold  and 
silver. 

The  result,  divided  by  two  or  thirty,  will 
give  the  number  of  parts  of  metallic  lead  that 
one  part  of  argol  is  able  to  reduce  from 
litharge.  It  ranges  around  8.5  parts. 

2.  Cream  of  Tartar,  or  bi-tartrate  of  potash 
(p.  133).  —  Same  charge  as  abo.ve,  excepting 
that  the  two  grammes  or  thirty  grains  of  argol 
are  to  be  replaced  by  three  grammes  or  forty- 


1 6  2  MANUAL    OF  ASSA  YING. 

five  grains  of  the  tartar.  One  part  of  pure 
tartaric  acid  will  reduce  6  parts  of  lead,  and 
the  same  amount  of  ordinary  cream  of  tartar 
will  reduce  6.4  parts  of  lead. 

j>.  Charcoal (p.  135). — Make  up  this  charge  : 
Bi-carb.  of  soda. .  2  A.  T.,  60  grms.,  960  grains  or  2  oz. 
Carb.  of  potash  ..J  "  7$  "  120  "  "|« 

Litharge 2     "       60      "       960        "       "   2   " 

Charcoal i  gramme  or  15  grains. 

Salt  cover. 

Use  an  "  S"  crucible.  As  previously  stated, 
the  reducing  power  of  one  part  of  charcoal 
varies  between  22  and  32  parts  of  lead. 

The  reducing  powers  of  the  other  sub- 
stances given  on  page  134  are  determined  in  a 
similar  manner  to  the  three  quoted  above, 
running  coals  and  coke  as  for  charcoal,  white 
sugar  as  for  cream  of  tartar,  flours,  starches, 
etc.,  as  for  argol,  etc. 

V.    DETERMINATION  OF  THE  OXIDIZING  POWER 

OF   NITRE  (NITRATE  OF  POTASH). 
Determine  the  oxidizing  power  of  the  fine, 
dry  salt  (p.  135)  by  the  following  charge  : 


TESTING   OF  RE-AGENTS.  163 

Bi-carb.  of  soda. .  2  A.  T.,  60  grms.,  960  grains  or  2  oz. 
Carb.  of  potash  .  .J-      "       yj-       "        120       "       "   J  " 

Litharge 2      "      60       "       960       "       "    2   " 

Charcoal i  gramme  or  15  grains. 

Nitre 5  grammes  or  75  grains. 

Salt  cover. 

Use  an  "S"  crucible,  and  treat  as  in  the 
previous  crucible  operations.  The  difference 
between  the  weight  of  the  lead  button  ob- 
tained and  that  found  in  the  assay  of  the 
charcoal,  divided  by  five  or  seventy-five,  will 
give  the  oxidizing  power  of  the  nitre,  per 
part.  It  is  about  four  parts. 


PART  II. 
ASSAYING 


PART   II. 
AS  SA  YI  N  G. 


CHAPTER    I. 
GOLD  AND  SILVER  ORES. 

OCCURRENCE. — Gold  is  found  in  large  quan- 
tities in  the  native  state,  designated  by  the 
various  names  of  free  gold,  flour,  leaf,  wire 
and  nugget  gold.  The  minerals  which  most 
frequently  carry  gold  are  oxide  of  iron,  pyrites 
of  iron  and  copper  (known  as  auriferous  sul- 
phurets),  arsenopyrite,  and  tellurium  ores ;  of 
these,  the  most  abundant  are  the  first  two. 

Minerals  which  less  frequently  are  gold- 
bearing,  are  galena,  blende,  gray  copper  and 
"  carbonate  ores." 


1 68  MANUAL    OF  ASSAYING. 

For  a  classification  of  silver  ores  I  quote 
from  Kustel's  "  Roasting  of  Gold  and  Silver 
Ores": 

"  IMPORTANT    SILVER    ORES. 

The  most  important  silver  ores  are  those 
found  in  such  quantities  as  to  be  an  object  of 
metallurgical  operations.  The  principal  min- 
erals of  this  kind  are  the  following  : 

A.  Silver  ores  with  2invariable  amount  of 
silver.  —  a.  Sulphuret  of  silver,  or  silver 
glance,  with  87  per  cent  of  silver.  It  is  of 
common  occurrence.  b.  Brittle  silver  ore 
(stephanite),  or  sulphuret  of  silver  and  anti- 
mony. This  mineral  contains  68  per  cent  of 
silver,  and  is  quite  common,  c.  Polybasite, 
sulphuret  of  silver,  antimony  and  some  ar- 
senic, with  75  per  cent  of  silver,  d.  Ruby 
silver.  The  dark  red  silver  ore,  or  antimonial 
variety,  with  59  per  cent,  and  the  light  red 
silver  ore,  or  arsenical  variety,  with  65  per 
cent  of  silver,  are  valuable  minerals.  e. 
Miargyrite,  sulphuret  of  silver  and  antimony; 
36.5  per  cent  of  silver,  f.  Horn  silver,  or 


GOLD   AND    SILVER   ORES.  169 

chloride  of  silver,  with  75  per  cent  of  silver. 
g.  lodic  and  bromic  silver  of  yellow  and  green 
colors. 

B.  Argentiferous  ores  with  variable  amount 
of  silver. — a.  Stromeyerite,  or  silver  copper 
glance,  a  sulphuret  of  silver  and  copper  con- 
taining up  to  53  per  cent  of  silver,  b.  Stete- 
feldite,  with  25  per  cent  of  silver,  is  an  oxide 
ore.  c.  Silver fahlore,  argentiferous  gray  cop- 
per ore.  It  contains  silver  in  very  variable 
proportions  up  to  31  per  cent.  This  ore  is 
quite  common,  and  for  this  reason  is  impor- 
tant. It  is  also  one  of  the  most  rebellious 
ores,  containing  copper,  antimony,  arsenic, 
sulphur,  lead,  iron,  zinc,  and  sometimes  gold 
and  quicksilver,  d.  Chloride  ores  (so-called), 
mostly  decomposed  ores,  generally  of  an 
earthy  appearance  and  different  colors.  They 
contain  more  or  less  finely  divided  chloride  of 
silver. 

C. — a.  Argentiferous  lead  ores,  galena,  or 
sulphuret  of  lead,  lead  glance.  "Generally,  this 
is  not  rich  in  silver,  containing  from  $20  to 


I7O  MANUAL   OF  ASSAYING. 

$60  per  ton.  Specimens  assay  sometimes  as 
high  as  $300.*  b.  Cerussite,  carbonate  of 
lead.  If  pure,  without  admixture  of  copper 
and  other  carbonates,  it  is  poor  in  silver  in 
most  cases,  c.  Argentiferous  zinc  blende,  sul- 
phuret  of  zinc.  Pure  zinc  blende  contains 
usually  only  traces  of  silver  ;  often,  however, 
it  assays  well,  even  up  to  $400  per  ton.  d. 
Argentiferous  pyrites.  Copper  and  iron  py- 
rites are  poor  in  silver,  but  often  auriferous. 

There  are,  besides,  numerous  classes  of 
decomposed  silver  ores,  generally  of  earthy 
nature ;  also,  half  decomposed  ores  which 
have  lost  their  metallic  glance,  having  a  black 
or  bluish-black  color,  and  being  generally 
cupriferous."  f 

ASSAY. — We  can  best  consider  the  system- 
atic fire  treatment  of  gold  and  silver  ores,  by 
dividing  it  into  a  series  of  operations,  and 
taking  each  in  turn  and  in  detail. 

*  I  have  found  them  as  high  as  $1,500  per  ton.     (W.  L.  B.) 
f  See  appendix  for  extended  lists  of  the  minerals  of  or  contain- 
ing gold  and  silver. 


GOLD  AND    SILVER   ORES. 


The  three  main  divisions  are  : 

I.  Preparation  of  the  sample. 

II.  Scorification  process. 

III.  Crucible  process. 

I.     PREPARATION    OF    THE    SAMPLE. 

The  first  thing  to  be  done  in  the  treatment 
of  an  ore,  whether  it  is  to  be  assayed  for  gold, 
silver,  copper,  lead,  or  any  other  metal,  is  to 
place  it,  that  is,  to  label  it.  This  is  best  ac- 
complished by  giving  to  it  a  running  number, 
never  to  be  repeated.  By  adopting  this  sys- 
tem of  numbering  all  samples,  any  danger  of 
confusing  specimens  from  various  mines  or 
parts  of  the  same  mine  or  vein,  is  entirely 
gotten  rid  of.  Have  a  notebook  at  hand, 
and,  in  it,  under  the  number,  write  such  items 
as  may  be  necessary  or  useful,  as  the  date 
when  sample  was  received,  name  of  person 
sending  it,  character  of  the  ore,  nature  of  the 
charge,  weights  employed,  calculations,  etc. 
To  pieces  of  the  ore  which  are  to  remain 
whole,  affix  gummed  labels,  bearing  the  same 


172  MANUAL  OF  ASSAYING. 

number.  To  preserve  the  final  pulverized 
samples,  bottles  of  about  four  ounces  capacity, 
cork-stoppered,  and  similarly  labelled,  can  be 
employed,  or  what  is  even  better,  pasteboard 
boxes  in  size  about  5^  inches  long  by  3^ 
inches  wide  and  2  inches  high,  will  be  found 
to  be  very  serviceable.  They  can  be  written 
on,  thus  requiring  no  labels. 

The  next  step  is  to  secure  an  average  sample 
for  assay,  and  its  importance  cannot  be  over- 
rated. An  ore  is  by  no  means  of  uniform 
character,  being,  in  general,  made  up  of  the 
gangue  or  valueless  portion  of  the  ore,  through 
which  are  scattered  the  valuable  minerals. 
Therefore,  unless  the  sample  finally  chosen 
for  assay  represents  an  average  of  the  entire 
lot,  being  a  mixture  in  the  same  proportions, 
of  the  richest,  the  medium  and  the  poorest 
portions,  as  in  the  original  ore,  the  assay  itself 
is  worthless,  no  matter  how  carefully  it  may 
have  been  performed.* 

*  In  this  connection,  I  would  refer  the  student  to  an  article 
"On  the  Commercial  Sampling  of  Minerals, "by  Mr.  L.  S.  Austin, 
of  Salt  Lake  City,  Utah,  which  appeared  in  the  "Engineering  and 
Mining  Journal"  (July  22,  Aug.  5,  Aug.  26,  and  Sept.  16,  1882). 


GOLD   AND   SILVER    ORES.  173 


To  illustrate  the  averaging,  take  a  quantity 
of  ore  weighing  fifty  pounds,  which  may  be  as 
a  single  lump,  or,  better,  the  result  of  the 
selection  of  samples  across  a  section  of  the 
vein.  In  order  to  get  a  fair  average,  it  is  not 
necessary  to  operate  on  a  larger  quantity  than 
this  amount,  for  above  it,  should  come  in,  as 
a  more  practical  test,  the  mill-run. 

With  a  heavy  sledge-hammer,  break  up  the 
entire  mass  into  pieces  of  about  the  size  of  a 
hickory-nut.  Should  the  rocks  be  so  large  or 
so  very  hard  as  to  obdurately  resist  the  ham- 
mer, they  may  be  brought  into  submission  by 
that  process  called  "  astonishing,"  by  Prof. 
Chapman,  in  his  valuable  little  work.  It  con- 
sists in  heating  red-hot  the  resisting  pieces, 
and  plunging  them  while  thus  into  some  cold 
water  in  a  pan.  This  heroic  treatment  will 
either  at  once  reduce  the  lump  to  small 
pieces,  or  render  it  so  friable  that  light  pound- 
ing will  pulverize  it.  Pour  off  the  water  and 
dry  the  contents  thoroughly,  th'en  break  into 
small  pieces  as  directed.  Transfer  to  a  large 


174  MANUAL   OF  ASSAYING. 

sheet  of  heavy  brown  or  manilla  paper,  then, 
with  a  large  iron  or  steel  spatula,  thoroughly 
mix,' by  turning  over  and  over  and  by  stirring 
in  together  with  the  dust,  the  finer  and  coarser 
particles,  till  satisfied  that  the  whole  is  a 
homogeneous  mixture. 

(At  this  stage  of  the  operation  it  is  a  good 
plan  to  reserve  a  characteristic  lump  or  a  few 
pieces,  from  an  examination  of  which  the 
nature  of  the  ore  may  be  determined,  and 
process  of  treatment  decided  upon.) 

Now  divide  in  halves  by  means  of  a  very 
large  spatula  or  piece  of  heavy  sheet  brass,  18 
inches  long  by  4  inches  wide,  and  -J-inch  thick. 
Break  up  still  finer  (to  the  size  of  a  hazel-nut 
or  less)  the  half  selected.  Mix  again  and 
halve  as  before.  Continue  the  crushing,  mix- 
ing and  halving  until  about  one  pound  has 
finally  been  sampled  down. 


[57 


FIG.  90. 


GOLD  AND   SILVER   ORES.  175 

Instead  of  halving,  the  piles  may  be  quar- 
tered, and  two  of  the  diagonally  opposite 
quarters  taken  as  a  half.  Fig.  90  shows  the 
pile  entire,  divided,  quartered,  and  two  of  the 
quarters  removed ;  parts  i  and  4,  or  2  and  3, 
are  to  be  put  together. 

When  the  ore  to  be  assayed  is  less  than 
fifty  pounds,  ranging  down  to  a  pound  or  two, 
it  can  be  broken  still  smaller  in  the  successive 
steps,  and  when  it  is  but  a  few  ounces  in 
weight,  the  whole  of  it  should  be  crushed  and 
pulverized,  as  directed.  Wet  or  damp  ores 
and  pulps  should  be  dried  before  pulverizing. 

The  student  must  exercise  his  judgment  in 
a  measure,  with  regard  to  the  sampling  of  an 
ore,  simply  remembering  that  the  object,  as 
before  stated,  is  to  obtain  a  final  product 
which  shall  be  an  exact  counterpart,  in  rela- 
tive proportions,  of  the  metals  and  gangue  of 
the  original  ore. 

Instead  of  halving,  the  broken  ore  may  be 
taken  up  on  a  sampling  shovel,  and  thrown 
on  a  tin  or  copper  sampler,  making  it  a  rule 


I  76  MANUAL    OF  ASSA  YING. 

to  reject  either  all  that  which  goes  between 
the  prongs  or  ribs,  or  that  which  remains  up- 
on them.  These  two  articles  are  convenient, 
but  not  necessary. 

The  third  step  is  to  pulverize  the  sample 
finally  obtained,  which  may  be  done  very  sim- 
ply though  somewhat  laboriously  (depending 
considerably  upon  the  nature  of  the  ore),  by 
means  of  an  iron  mortar  and  pestle.  A  towel 
wrapped  loosely  around  the  pestle  and  across 
the  top  of  the  mortar  will  prevent  loss  due  to 
flying  particles. 

Sift  through  a  sieve  of  eighty  or  ninety  or 
even  of  one  hundred  meshes,  since  the  finer 
the  powder,  the  more  quickly  will  it  be  acted 
upon  in  the  furnace.  Ores  which  contain 
much  clay  or  lime  are  very  apt  to  clog  the 
meshes  of  the  sieve  so  that  little  will  pass 
through.  This  may  generally  be  obviated  by 
placing  in  the  sieve  an  ounce  weight  or  equal- 
ly heavy  piece  of  smooth  iron,  the  movement 
of  which  in  shaking  keeps  the  meshes  open. 
Do  the  sifting  over  a  piece  of  brown  paper, 


GOLD   AND   SILVER    ORES.  177 

and  be  sure  that  all  the  sample  passes 
through  the  sieve,  for  the  few  minute  parti- 
cles or  scales,  that  might  remain  on  the  sieve 
and  be  hastily  thrown  away,  could  be  of  suffi- 
cient value  to  vitiate  the  assay.  I  might  give 
here,  however,  a  little  suggestion  made  me  by 
Mr.  H.  H.  Corbin,  of  Telluride,  Colo.  Cer- 
tain ores  contain  free  silver  (with  a  little  gold 
in  it,  sometimes),  to  such  an  extent  that  while 
they  will  not  produce  many  scales,  yet  there 
may  be  a  few  left  on  the  sieve.  In  such  cases 
dump  the  scales  on  the  grinding  plate  and 
cover  them  with  the  finely-powdered  ore  which 
has  already  gone  through  the  sieve.  Grind 
heavily  for  quite  a  little  while,  then  sieve 
again.  It  will  be  found  that  most  of  the 
scales  have  been  ground  by  the  ore  (particu- 
larly when  the  latter  is  quartzose),  fine 
enough  to  go  through  a  loo-mesh  sieve.  If 
they  will  not,  repeat  the  treatment  until  they 
will.  Three  grindings  will  usually  suffice. 
The  sievings  are  to  be  very  carefully  mixed. 
Even  all  this  trouble  is  less  than  that  of  the 


178  MANUAL    OF  ASSAYING. 

ordinary  scale  method  of  treating  ores  con- 
taining the  precious  metals  in  the  free  state. 
(See  in  appendix,  4<  Assaying  of  Ores  con- 
taining Free  Gold  or  Free  Silver".) 

Mix  again  the  fine  powder,  and  with  a  large 
brush  transfer  to  the  properly  marked  box  or 
bottle,  when  the  sample  is  ready  for  assay. 
Do  not  shake  the  box  or  bottle  between  the 
times  of  grinding  and  weighing,  as  this  tends 
to  cause  the  gold,  silver,  sulphurets,  or  other 
heavy  minerals  to  settle,  resulting  in  an  un- 
equal distribution  of  the  various  constitu- 
ents of  the  ore.  If  much  time  elapses  be- 
tween the  weighings  and  the  second  treat- 
ment the  ore  should  be  remixed. 

When  very  many  assays  have  to  be  per- 
formed daily,  the  rubbing-plate  and  rubbers 
will  be  found  so  very  convenient  and  so  time- 
and-labor-saving,  that  they  will  become  almost 
necessities.  (See  pp.  28-31  for  description.) 

The  operation  of  grinding,  or  rubbing,  or 
pulverizing,  is  managed  as  follows  :  The  ore, 
previously  broken  into  fine  pieces  as  directed, 


GOLD   AND    SILVER   ORES.  179 

is  placed  upon  the  clean  surface  of  the  plate, 
the  rocker  is  now  laid  upon  it,  and  with  one 
hand  firmly  pressed  upon  the  body  of  the 
rocker,  and  the  other  grasping  its  handle,  it  is 
moved  backward  and  forward  with  an  oscil- 
lating motion.  This  knack  of  grinding,  al- 
though not  easy  to  describe,  is  soon  acquired. 

After  grinding,  the  plate  should  be  thor- 
oughly cleaned,  which  can  be  done  by  rubbing 
on  it  either  sand,  quartz,  broken  glass,  com- 
mon salt,  old  cupels  or  scorifiers,  broken  cru- 
cibles, the  slags  from  scorifications,  or  some 
worthless  ore,  finishing  with  an  old  rag.  Very 
great  pains  should  be  taken  to  perfectly  clean 
the  plate  after  grinding  much  free  gold  ore  or 
such  rich  ores  as  tellurides. 

In  place  of  the  sheets  of  brown  paper  al- 
ready mentioned,  and  which  quickly  become 
soiled  and  full  of  holes,  the  zinc  sifting-pans 
(p.  35,  fig.  13)  can  be  used  to  advantage. 

To  guard  against  loss  of  dust,  the  tin  box- 
sieve  (p.  34)  is  recommended.  There  is  an- 
other laboratory  plan  for  systematic  sampling, 


ISO  MANUAL    OF  ASSAYING. 

which  is  very  fair,  though  slow  and  best  suited 
for  small  lots  of  from  5  to  20  pounds  of 
ore.  For  this  the  assayer  needs  four  sieves 
in  addition  to  the  fine  one  —  they  are  4,  8,  16 
and  32-mesh,  respectively. 

Crush  the  sample  so  that  it  will  just  about 
go  through  the  4-mesh  sieve,  mix  thoroughly, 
divide  in  halves,  reject  one-half,  and  crush 
the  remainder  so  it  will  just  pass  through  the 
8-mesh  sieve.  Again  mix,  divide  in  halves, 
reject  half,  and  crush  the  other  half  for  the 
i6-mesh  sieve.  Mix,  halve,  reject  half,  and 
crush  for  the  32-mesh  sieve.  The  half  kept 
from  this  is  all  to  be  pulverized  and  put 
through  the  loomesh.  All  this  insures 
thorough  mixing  and  uniform  crushing  and 
sampling. 

Having  now  finely  ground  the  ore  to  be 
assayed,  we  must  next  decide  how  to  treat  it. 

There  are  two  methods  of  assaying  gold 
and  silver  ores,  the  scorification  and  the  cru- 
cible. 

The  process  to  be  chosen  depends  chiefly 


GOLD   AND    SILVER    ORES.  l8l 

on  the  nature  of  the  ore.  In  general,  we  may 
say  the  scorification  process  is  better  adapted 
for  all  silver  ores,  and  for  rich  gold  ores  (in- 
cluding telluride  ores  of  any  degree  of  rich- 
ness). 

The  crucible  process  serves  better  for  low 
grade  gold  ores.  The  advantage  of  this  pro- 
cess lies  mainly  in  the  fact  that  it  enables  us 
to  operate  upon  a  larger  quantity  of  ore;  oth- 
erwise it  is  no  better  than  the  scorification 
method  and  indeed  in  many  respects  the  lat- 
ter is  to  be  preferred. 

The  scorification  process  is  so  much  simpler 
to  use,  easier  to  comprehend,  and  so  satis- 
factory in  its  working,  that  I  shall  give  it  the 
first  place  in  this  manual. 

II.      SCORIFICATION    PROCESS. 

The  object  of  this  process  is  to  so  act  upon 
an  ore  with  heat,  access  of  air,  and  certain 
re-agents,  that  the  precious  metals  shall  be 
driven  out  of  their  combinations  with  the 
impurities  of  the  ore  (or  if  free,  separated 


I  8 2  MA NUAL    OF  A SSA  YING. 

from  them),  and  be  retained  alloyed  with 
another  metal,  lead,  and  from  which  they  can 
afterwards  be  separated. 

The  chief  re-agents  are  lead,  in  a  granu- 
lated condition,  and  borax  glass. 

Besides  these,  silica,  iron,  and  bi-carbonate 
of  soda  are  occasionally  employed. 

The  ore,  mixed  with  the  1'ead,  and  covered 
with  the  borax  glass  or  other  flux,  is  put  into 
a  scorifier  and  subjected  to  heat  in  a  muffle. 

Under  the  action  of  the  heat,  the  lead 
melts,  and  being  scattered  throughout  the 
ore,  seizes  upon  the  gold  and  silver  and  set- 
tles with  them  to  the  bottom  of  the  scorifier. 
The  borax  o-lass  or  other  flux  attacks  the 

o 

gangue  and  impurities  present,  and  uniting 
with  them  and  with  litharge  resulting  from 
oxidation  of  some  of  the  lead,  forms  a  slag  or 
glass,  which  floats  upon  the  surface  of  the 
molten  lead. 

So  much  for  the  theory  of  scorification;  in 
practice  we  follow  in  regular  rotation  the 
steps  here  given: 


GOLD  AND   SILVER   ORES.  183 

a.  Preparation  of  Charge  (including  weigh- 
ing   of   ore,  roasting,  weighing  of  re-agents, 
mixing,  etc). 

b.  Scorification. 

c.  Cupellation. 

d.  Weighing  the  Gold  and  Silver  Bead. 

e.  Parting. 

f.  Inquartation. 

g.  Weighing  the  Gold  Residue. 
h.   Calculations-. 

a.  Preparation  of  Charge. 

Whatever  subsequent  treatment  an  ore  is 
to  undergo,  the  quantity  required  for  assay 
must  be  weighed  first.  Certain  ores  may 
possibly  be  subjected  to  a  preliminary  opera- 
tion known  as  roasting,  but  the  ore  must  be 
weighed  out  before  this,  not  after. 

If  the  ore  in  question  is  in  a  bottle,  pour  all 
out  upon  a  clean  piece  of  black  glazed  paper  or 
piece  of  sheet  rubber,  or  if  it  is  in  a  box,  it  can 
be  sampled  therein.  Weigh  the  amount  de- 
sired, sampling  from  various  parts  of  the  ore.. 


184  MANUAL    OF  ASSAYING. 

Have  ready  cleaned  a  number  of  the  scori- 
fiers.  Number  or  letter  each  scorifier  with 
ruddle  (liquid  or  lump),  weigh  the  requisite 
amount  of  granulated  lead,  divide  approxi- 
mately in  halves,  and  transfer  one-half  to  the 
scorifier.  Upon  it  brush  the  ore  (roasted  or 
not)  and  mix  by  means  of  a  small  steel  spatula. 
Pour  the  remaining  half  of  the  lead  evenly 
over  the  surface  of  the  mixed  ore  and  lead, 
and  over  all  sprinkle  the  borax  glass.  In  simi- 
lar manner  prepare  all  the  other  charges. 

A  deviation  from  this  method  has  been  fol- 
lowed by  some  assayers.  Their  procedure  is 
to  put,  say,  \  of  the  lead  at  the  bottom  of  the 
scorifier,  then  the  ore  and  \  of  the  lead  mixed 
previously,  topping  all  with  the  remaining  \  of 
the  lead.  This  change  is  due  to  the  fear  of 
unacted-upon  ore  remaining  at  the  bottom  of 
the  scorifier.  I  am  inclined  to  consider  it  an 
almost  unnecessary  refinement. 

In  many  assaying  establishments,  notably 
the  larger  ones,  the  practice  of  marking  scori- 
fiers,  cupels,  and  crucibles  does  not  obtain. 


GOLD   AND    SILVER   ORES.  185 

Instead  of  this,  a  systematic  order  of  arrang- 
ing these  articles  is  kept  up,  either  in  or  out  of 
the  furnace,  and  this  routine  of  position  and 
order  of  working  is  never  varied,  so  that  by 
relative  place  a  sample  can  always  be  identi- 
fied. This  plan  is  indeed  a  good  one,  and 
perhaps  imperative  where  very  much  work  is 
done,  but  for  the  beginner,  for  a  time  at  least, 
the  custom  of  marking  everything  had  better 
be  adopted. 

CHARGES. 
(For  manner  of  roasting  see  "  III.     Crucible  Process.") 

1.  One  for  "every  day"  ores,  serving  well 
for  the   common    run   of    ores   in   which    the 
metals  are  not  in  excess  of  the  gauge,  is  the 
following: 

Ore \  A.  T. ,     5  grammes,     96  grains  or  \  oz. 

Granulated  lead i^      "       45  720          "       i^  " 

Borax  glass 250  mgrms.,  or  4  grains. 

Use  it  for  ores  that  do  not  contain  much 
copper  or  lead. 

2.  Copper  glance  or  copper  pyrites  : 

Ore    -jJjj-  A.  T.,  2^  grammes,      48  grains  or  TJ7  oz. 

Granulated  lead  .  . .     2|      "75  "         1,200          "         2^  " 

Borax  glass    200  mgrms.,  or  3  grains. 


I  86  MANUAL   OF  ASSAYING. 

For  the  above  ores,  a  preliminary  roasting 
can  be  made,  if  considered  advisable. 

If  not  to  be  roasted,  and  when  there  is  not 
very  much  of  the  sulphurets  present,  heat 
gently  for  a  time,  till  the  roasting  in  the  scori- 
fier  is  done. 

If  rich  in  sulphurets,  a  strong  heat  can  be 
applied  at  once,  melting  everything  down  into 
a  sort  of  matte,  then  proceeding  as  usual. 

3.  Copper  matte: 

Matte   Y1^  A.  T.,    2^  grammes,      48  grains  or  r\y  oz. 

Granulated  lead  ....  3       "       90  1,440          "         3    ' 

Use  no  borax  glass  ;  instead  : 

Powdered  silica ^V  A.  T.,  i|  grammes,  24  grains  or  -£rf  oz. 

4.  Gray  copper  ores  : 

Ore Y1^  A.  T.,    2|  grammes,    48  grains  or  ^  oz. 

Granulated  lead 2       "       60  960  "         2    " 

Borax  glass 300  mgrms.,  or  5  grains. 

5.  Sulphurets  of  iron  : 

Ore \  A.  T.,     7 1  grammes,     120  grains  or    \  oz. 

Granulated  lead i\      "       75  1,200          "        o.\  " 

Borax  glass 200  mgrms.,  or  3  grains. 

Litharge  can  be  used  to  advantage  in  this 
as  in  other  unroasted  sulphurets. 


GOLD   AND    SILVER   ORES.  187 

Always  weigh  the  litharge,  so  as  to  allow 
for  its  contained  silver. 

6.  Oxide  of  iron  : 

Ore  \  A.  T.,    5  grammes,     96  grains  or    \  oz. 

Granulated  lead i^      "      45          "  72o  Ji   " 

Silica i         "    'or    15^ 

Borax  glass 350  mgrms.,  or  5-|  grains. 

The  silica  to  be  mixed  with  the  charge — it 
can  be  diminished  as  the  percentage  of  silica 
in  the  ore  increases. 

7.  Galena : 

Ore  £  A.  T. ,  15  grammes,  240  grains  or    |  oz. 

Granulated  lead i|       "       45  "         720          "         i£  " 

Borax  glass 100  mgrms.,  or  i|  grains. 

Gentle  heat.  A  nail  in  the  scorifier  aids  in 
the  desulphurization. 

8.  "  Carbonate"  ores  : 

Ore I  A.  T.,    5  grammes,    96    grains  or  £  oz 

Granulated  lead .2      "       60          "          960  "        2   " 

Borax  glass |  gramme  or  7^  grains. 

9     "Chloride"  ores  : 

Ore i  A.  T.,     5  grammes,     96  grains  or    £  oz. 

Granulated  lead i^      "      33          "          576         "         i£  " 

Borax  glass 300  mgrms.,  or  5  gfains. 

Use  as  low  a  heat  as  possible    until    the 


1 88  MANUAL    OF  ASSAYING. 


charge    has    covered    over,    then    heat    more 
strongly  to  complete  fusion. 

10.  Blende  : 

Ore  |  A.  T.,     5  grammes,      96  grains  or  \  oz. 

Granulated  lead .. 3       "       90         "          1,440         "        3  " 

Borax  glass 400  mgrms.,  or  6  grains. 

Needs  a  good  heat  and  care  in  its  assay. 

1 1.  Arsenical  and  antimonial  ores  : 

Ore £  A.  T.,       5  grammes,      96  grains  or  £  oz. 

Granulated  lead 4      "       120          "        1,920          "         4  " 

Borax  glass i|  grammes  or  23  grains. 

This  charge  may  have  to  be  divided  — 
sometimes  requires  several  re-scorifications. 
A  piece  of  charcoal  laid  over  the  scorifier,  or 
some  of  it  pulverized  and  dropped  therein, 
often  aids  the  fusion,  as  has  been  previously 
remarked. 

12.  Tellurides.: 

Ore   •£$  A.  T.,    2^  grammes,    48  grains  or  T^  oz. 

Granulated  lead 2       "       60  "  960  "         2    " 

Litharge TV     "       2$  "  48 

Borax  glass 250  mgrms. ,  or  4  grains. 

Sprinkle  the  litharge  over  the  mixed 
charge.  The  buttons  may  need  repeated 
scorifications  with  plenty  of  lead  (20  to  i). 


GOLD   AND   SILVER   ORES.  189 


13.  Native  gold  or  silver,  or  very  rich  ores 
of  any  kind  : 

Ore TV  A.  T.,     2|  grammes,    48  grains  or  T^  oz. 

Granulated  lead \\       "        45  "  720          "        \\    " 

Borax  glass 250  mgrms.,  or  4  grains. 

Ores,  either  those  already  described  or  any 
others,  having  a  great  quantity  of  lime  or 
baryta,  will  require  more  borax  glass  than  the 
quantities  given.  It  may  need  to  be  as  much 
as  the  ore  taken  —  in  such  cases  the  charge 
may  have  to  be  divided,  and  several  scorifica- 
tions  and  re-scorifications  made.  Such  large 
quantities  of  borax  are  best  added  at  inter- 
vals, not  at  the  beginning.  Stirring  will  often 
aid.  Give  a  strong  heat.  Make  use  of  silica 
also. 

The  weights  of  borax  glass  are  put  down 
more  to  serve  as  indications  than  for  precise- 
ness'  sake.  It  need  not  be  weighed  at  all ; 
after  a  time  the  assayer  will  learn  to  use  it  in 
pinches. 

Study  and  experiment  are  necessary  here. 
Ores  will  be  found  made  up  of  several  of 
those  given  separately  above  —  new  combina- 


IQO  MANUAL    OF  ASSAYING. 

tions  of  minerals  are  constantly  coming  to 
light. 

The  operator  must  then  work  over  the  par- 
ticular ores  he  comes  in  contact  with,  until  he 
learns  them  thoroughly. 

The  colors  shown  by  the  interiors  of  scori- 
fiers  are  often  characteristic  of  the  ores 
tested,  and  in  conjunction  with  the  colors  of 
the  cupels  after  cupellation  make  valuable 
tests.  The  following  descriptions  may  per- 
haps be  of  some  value  to  the  student  in  this 
connection  : 

.    COPPER. 

Scarifier  (See  color  plate). — A  green,  more 
or  less  deep,  according  to  the  percentage  of 
this  metal.  Where  the  coating  is  somewhat 
thick,  as  on  the  edges  of  the  scorifier,  the 
color  becomes  a  dark  brown,  but  the  prevail- 
ing tint  is  green. 

Ciipel. —  Slate  green,  ranging  to  blackish 
green  —  prevailing  tint  very  dark  blackish 
green.  There  is  frequently  a  rose  coat  on  the 


SCORIFIER 
COLORS. 


COPPER. 


IRON. 


LEAD. 


MANGANESE. 


CHROMIUM. 


URANIUM. 


GOLD  AND   SILVER   ORES.  IQI 

outside  of  cupels  from  ores  rich  in  copper, 
which  need  not  be  mistaken  for  the  rose  color 
of  oxide  of  silver.  This  rose  tint  meeting  the 
slate  green  produces  a  purplish  black  or  purp- 
lish green. 

IRON. 

Scarifier  (See  color  plate). —  With  large 
amounts  of  iron  the  interior  is  black  with  a 
gray  metallic  lustre  (this  indicates  a  poor 
fusion),  from  which  the  color  ranges  down 
through  a  deep  rich  mahogany  and  varying 
shades  of  red-brown  to  a  light  yellow-brown. 
A  red-brown  is,  however,  always  present,  and 
is  the  prevailing  color. 

Cupel. —  A  brown  tint,  more  or  less  decided. 

LEAD. 

Scarifier  (See  color  plate). — Various  shades 
of  lemon  yellow. 

(Vanadium,  cadmium,  and  bismuth  give 
same  shades.) 

CupeL —  Bright,  rich  yellow  to  lighter 
shades. 


1 92  MANUAL   OF  ASSAYING. 


(Small  amounts  of  antimony,  arsenic,  bis- 
muth, cadmium  or  zinc  retained  in  the  button 
also  leave  yellow  markings  on  the  cupel.) 

MANGANESE. 

Scarifier  (See  color  plate). — From  a  purple- 
black  to  a  light  violet-brown  or  amethyst 
color. 

Cupel. —  Blackish  green  to  a  lighter  green, 
usually  the  latter.  It  is  never  so  deep  nor 
the  cupel  so  thoroughly  permeated  by  the 
color  as  is  the  case  with  copper  ;  the  color 
also  is  different. 

CHROMIUM. 

Scarifier  (See    color  plate). —  Blood-red  - 
thicker  portions  of  the  glaze  a  green,  but  pre- 
vailing tint  is  an  orange  or  blood  red. 

Cupel. — Lemon-yellow,  with  reddish  edges, 
surface  also  somewhat  mottled  with  reddish- 
brown  blotches  —  characteristic  appearance. 
NICKEL. 

Scarifier. —  A  dirty,  brownish  yellow,  and 
not  very  characteristic.  A  lead  ore  with  a 
little  iron  would  imitate  it  exactly. 


GOLD   AND    SILVER    ORES.  193 

Cupel. — Brown,  almost  identical  with  iron. 

URANIUM. 

Scarifier  (See  color  plate). — A  peculiar  red. 
Cupel. — Brown,  as  for  iron. 

COBALT. 

Scarifier.  —  A  beautiful  blue  ;  toward  the 
bottom  it  struggles  with  a  green,  which  is 
probably  due  to  the  union  of  the  yellow  oxide 
of  lead  and  the  cobalt  blue.  This  color  will 
not  be  obtained  from  any  ore,  but  it  is  proba- 
ble that  it  has  its  effect  in  modifying  other 
colors. 

Cupel. — Brown,  as  for  iron. 

TELLURIUM. 

Scarifier. — A  yellowish  color,  with  some  red 
spots  ;  not  very  characteristic. 

C^lpeL — Yellow,  with  small  green  stains. 

It  must  be  borne  in  mind  that  combinations 
of  the  metals  are  liable  to  influence  these  col- 
ors and  to  produce  mixed  shades. 

Also  both  the  scorifier  and  cupel  must  be 
examined,  not  one  alone,  for  the  scorifier  may 


1 94  MANUAL    OF  ASSAYING. 

reveal  one  metal,  the  cupel  another.  Thus 
an  ore  containing  about  equal  parts  of  copper 
and  iron  gives  a  red-brown  in  the  scorifier,  in- 
dicating iron,  while  the  green  of  the  copper  is 
almost  entirely  masked.  On  the  other  hand, 
the  cupel  is  green-black,  indicating  copper, 
while  no  brown  of  the  iron  is  visible;  hence 
both  tests  prove  both  metals  to  be  present  in 
the  original  ore. 
b.  Scarification. 

Place  the  scorifiers,  by  means  of  the  scori- 
fier tongs  (page  94,  fig.  43)  in  the  middle  and 
back  of  the  muffle,  which  should  be  decidedly 
hot,  close  the  door  and  augment  the  draft. 

Then  begins  the  first  operation,  the  melting 
or  fusion  of  the  lead,  due  to  intense  heat  and 
absence  of  oxygen,  which  takes  from  three  to 
four  minutes. 

When  the  lead  is  liquid,  open  the  door,  thus 
admitting  a  current  of  air  to  supply  oxygen, 
and  which  will  also  tend  to  diminish  the  heat 
somewhat. 

Now,  in  the  case  of  ores  containing  or  re- 


GOLD  AND    SILVER   ORES.  195 

taining  antimony,  arsenic,  sulphur,  or  zinc,  a 
second  operation,  roasting,  begins  and  con- 
tinues till  the  greater  proportion  of  the  sub- 
stances named  have  volatilized,  the  remainder 
of  them  going  into  the  slag. 

During  this  time  the  borax  glass  has  melted 
and  begun  uniting  with  the  gangue  of  the  ore 
and  with  oxide  of  lead  to  form  a  slag  which 
surrounds  as  a  ring  the  molten  lead. 

As  the  scorification  goes  on,  the  melted 
lead  grows  smaller  and  smaller  by  oxidation 
and  the  volatilization  of  the  greater  part  of 
the  oxide  formed,  while  the  ring  of  slag  grad- 
ually closes  in  and  finally  covers  the  lead, 
which  is  seen  no  more. 

Finally  increase  the  heat  for  a  minute  or 
two  to  fully  liquefy  the  slag,  which  will  finish 
the  process  of  scorification. 

Remove  the  scorifiers,  and  pour  their  con- 
tents into  the  cups  of  the  scorification  moulds 
(page  99,  figs.  53  and  54),  which  should  not  be 
cold,  covering  each  receptacle  with  its  proper 
scorifier  to  retain  its  identification.  (If  neces- 


ig6  MANUAL  OF  ASS  A  YING. 

sary,  these  scorifiers  can  be  again  employed 
for  ores,  etc.) 

After  having  poured  the  charge,  it  will  be 
well  to  let  the  slag  and  button  remain  in  the 
cavity  of  the  mould  until  they  are  stone  cold 
before  dumping  them  out,  as  otherwise  there 
is  danger  of  the  lead  adhering  firmly  to  the 
slag. 

Instead  of  pouring,  the  leads  can  be  allowed 
to  cool  in  their  scorifiers,  but  no  advantage  is 
gained  by  this,  and  they  take  a  longer  time  to 
cool. 

In  either  case,  however,  when  cold,  detach 
the  lead  buttons  from  their  slags,  and  hammer 
each  button  into  a  clean  cube  with  flat- 
••  tened  .corners  (fig.  91).  Were  the 
FIG.  91.  corners  to  be  left  sharp,  they  would 
injure  the  cupel  when  the  button  came  to  be 
dropped  into  it. 

The  weight  of  the  button  will  vary  accord- 
ing to  the  conditions  ;  the  nature  of  the  ore, 
the  size  of  the  charge,  the  heat  of  the  furnace 
and  the  length  of  time  the  charge  was  allowed 


GOLD  AND   SILVER   ORES.  197 

to  remain  in  it,  all  exert  an  influence.  A  good 
weight  is  from  twelve  to  sixteen  grammes, 
which  will  make  a  cube  of  about  one-half  inch. 

The  button  of  lead  is  to  be  marked  with 
some  identifying  number  or  letter  with  the 
point  of  a  file  or  knife-blade. 

The  button  should  be  perfectly  malleable  ; 
if  brittle  it  has  probably  retained  antimony, 
arsenic,  zinc  or  litharge,  which  can  be  gotten 
rid  of  by  re-scorification.  But  with  ores  very 
rich  in  gold  proceed  with  care,  for  the  brittle- 
ness  may  be  due  to  the  gold  itself,  as  beyond 
a  certain  limit  gold  takes  away  from  the 
malleability  of  lead.  If  the  button  is  large  no 
extra  lead  need  be  added;  if  small  an  assay 
ton  or  two  may  be  melted  with  it. 

Again,  the  button  may  be  very  hard  on  ham- 
mering or  show  red  in  places,  and  perhaps  on 
taking  out  of  the  scorification  mould  may 
have  mossy  copper  on  the  bottom.  In  such 
cases  the  button  must  be  re-scorified  until  no 
more  copper  is  seen,  or  until  it  is  very  malle- 


198  MANUAL    OF  ASSAYING. 

able.  Plenty  of  lead  must  be  used  to  alloy 
with  the  copper. 

Since  there  is  a  greater  loss  of  silver  by 
cupellation  than  in  scorification,  very  large 
buttons  should  be  scorified  down  to  a  size 
suited  to  the  cupels. 

Examine  the  slag,  and  if  it  contains  any 
globules  of  lead,  hammer  them  flat,  then  place 
them  on  top  of  the  main  button,  and  cupel  all 
together. 

The  slag  should  be  vitreous  or  glassy,  and 
of  uniform  character,  its  color  depending  upon 
the  nature  of  the  ore. 

The  scorifier  should  be  perfectly  smooth  in 
its  interior,  that  is,  it  should  have  no  semi- 
fused  lumps  adhering  thereto.  Occasionally 
it  may  be  corroded  or  eaten  away,  which  does 
not  necessarily  injure  the  assay,  unless  the 
corrosion  extends  through  the  dish  and  allows 
its  contents  to  flow  out  upon  the  floor  of  the 
muffle.  In  such  a  case  (when  of  course  the 
assay  must  be  repeated)  at  once  cover  the 
floor  of  the  muffle  with  dry  sand  or  bone-ash, 


GOLD  AND    SILVER   ORES. 


199 


using  the  muffle  shovel  (fig.  51),  and  scrape 
out  the  mass  adhering  to  it  by  means  of  the 
hoe  or  scraper  (fig.  55).  If  this  cleaning 
out  of  the  muffle  after  an  accident  by  spilling 
or  leakage  is  not  attended  to,  it  leads  to 
either  one  or  both  of  two  evils  :  first,  the 
melted  lead  and  borax  attack  the  muffle  and 
rapidly  eat  a  hole  through  it ;  secondly,  they 
stick  to  any  scorifier  or  cupel  placed  in  the 
muffle,  making  it  almost  impossible  to  move 
or  remove  either  without  breakage  or  loss  of 
contents. 

The  corrosion  of  the  scorifier  is  a  good  hint 
to  add  silica  to  similar  ores,  for  usually  it  is 
the  lack  of  this  in  the  ore  that  causes  the 
abstraction  of  silica  from  the  scorifier,  though 
there  are  times  when  a  mixture  of  much  lead 
and  little  ore  is  being  scorified,  that  the  lith- 
arge formed  by  the  oxidation  of  the  lead  itself 
attacks  the  scorifier,  and  again,  as  in  case  of 
compounds  rich  in  copper  (a  copper  matte,  for 
instance),  the  oxide  of  cop'per  attacks  the 
scorifier. 


2OO  MANUAL   OF  ASSAYING. 

Sometimes  in  the  process  of  scorification  a 
crust  forms  over  the  surface  of  the  charge 
and  refuses  to  break.  Such  a  crust  is  gener- 
ally due  to  arsenical  and  antimonial  ores  pres- 
ent, and  may  often  be  destroyed  by  dropping 
in  the  scorifier  some  powdered  charcoal 
wrapped  in  a  wad  of  thin  paper. 

The  oxidation  can  also  be  commenced  by 
stirring  the  charge  with  a  bent  wire,  until  the 
lead  is  uncovered  and  begins  to  act.  Withdraw 
the  wire,  break  off  the  mixture  adhering  to  the 
end  and  return  it  (the  slag,  etc.)  to  the  scori- 
fier, as  it  will  probably  carry  some  of  the  ore. 
c.  Cupellation. 

This  operation  consists  in  oxidizing  the 
lead  of  the  lead  buttons,  the  litharge  formed 
by  the  heat  being  partly  absorbed  by  the 
cupel  and  partly  driven  up  the  chimney,  leav- 
ing the  gold  and  silver  together  as  a  bead 
upon  the  surface  of  the  cupel.  Other  metals 
that  may  have  remained  in  small  quantity 
from  the  previous  operations,  are  also  oxi- 
dized and  so  gotten  rid  of. 


GOLD  AND   SILVER   ORES.  2OI 

Take  a  good  cupel  (pages  107-1 10,  fig.  65), 
in  weight  about  one-third  greater  than  that  of 
the  button  that  is  to  go  in  it,  blow  out  any 
dust  or  impurities  from  the  interior,  mark  on 
its  sides  in  three  or  four  places  with  ruddle  or 
the  point  of  a  file,  its  appropriate  number  or 
letter,  and  with  the  aid  of  the  cupel  tongs  or 
cupel  shovel  and  hoe,  place  it  in  the  muffle  and 
there  let  it  remain  some  four  or  five  minutes 
that  it  may  acquire  the  temperature  of  the 
furnace. 

As  can  be  inferred  from  the  preceding 
paragraph,  the  size  of  the  cupel  depends 
upon  the  size  of  the  lead  button.  And  as 
mentioned  under  cupel-making,  it  is  a  good 
plan  to  have  on  hand  cupels  of  various 
weights.  It  is  stated  that  a  good  cupel  will 
absorb  its  own  weight  of  litharge,  and  further- 
more, it  is  able  to  take  a  button  heavier  than 
its  own  weight,  for  a  large  amount  of  litharge 
(or  oxide  of  lead)  is  driven  off  in  fumes  and 
consequently  does  not  enter  into  the  body  of 
the  cupel.  But  it  is  better  to  employ  a  cupel 


202  MANUAL   OF  ASSAYING. 

the  weight  of  which  is  from  one-fourth  to  one- 
third  more  than  that  of  the  button,  for  when 
a  cupel  becomes  nearly  saturated  with  litharge, 
the  cupellation  proceeds  too  slowly,  when,  on 
the  contrary,  it  ought  to  be  somewhat 
hastened,  and  cases  occur  that  the  cupellation 
ceases,  though  there  may  be  at  the  bottom  of 
the  cupel  enough  unattacked  bone-ash  to 
absorb  the  remaining  lead. 

At  other  times  an  assayer  may  carelessly 
put  altogether  too  large  a  button  in  a  cupel, 
and  therefore  all  the  bone-ash  in  the  cupel  be 
saturated  with  litharge  while  there  is  yet 
melted  lead  above;  This  error  may  some- 
times be  rectified  by  putting  a  second  cupel, 
red  hot  and  inverted,  under  the  soaked  cupel, 
when  the  cupellation  will  proceed,  though 
slowly.  But  it  is  better  to  reduce  by  scorifi- 
cation,  in  the  first  place,  the  excessively  large 
button. 

When  the  cupel  or  cupels  have  been  in  the 
muffle  a  few  minutes,  and  consequently  have 
become  of  the  same  temperature  as  the  inte- 


GOLD  AND    SILVER   ORES.  203 

rior  of  the  muffle,  the  lead  button  or  buttons 
are  to  be  placed  in  them,  each  one  in  its 
proper  cupel,  by  means  of  the  smaller  curved 
tongs  (page  94,  fig.  41),  and  the  muffle-door 
of  the  furnace  closed,  having  previously,  if 
necessary,  placed  a  couple  of  pieces  of  coke 
or  charcoal  in  the  mouth  of  the  muffle. 

If  the  muffle  has  been  of  the  proper  tem- 
perature, in  a  minute's  time  or  less,  all  the 
lead  buttons  will  have  quietly  fused,  and,  on 
opening  the  muffle-door,  each  will  be  seen  as 
a  little  lake  of  molten  metal,  from  which  arise 
fumes  of  oxide  of  lead. 

The  closing  of  the  door  at  first  is  simply  in 
order  to  melt  the  lead  buttons,  by  the  in- 
creased heat  and  absence  of  air. 

It  is  very  difficult  to  give  in  words  direc- 
tions for  the  proper  conducting  of  this  impor- 
tant step  of  cupellation.  Experience  is  the 
best  instructor. 

In  general,  do  not  have  the  furnace  too  hot. 
This  is  not  a  matter  of  so  much  importance 
in  the  cupellation  of  the  lead  buttons  from 


204  MANUAL   OF  ASSAYING. 

gold  ores,  but  in  those  from  rich  silver  ores  it 
is  such. 

"  The  heat  is  too  great  when  the  cupels  are 
whitish,  and  the  metallic  matter  they  contain 
can  scarcely  be  seen,  and  when  the  fume  is 
scarcely  visible  and  rises  rapidly  to  the  arch 
of  the  muffle"  (Mitchell),  and  particularly 
when  the  melted  lead  bubbles. 

"  The  heat  is  not  strong  enough  when  the 
smoke  is  thick  and  heavy,  falling  in  the  muffle, 
and  when  the  litharge  can  be  seen  not  liquid 
enough  to  be  absorbed,  forming  lumps  and 
scales "  (Mitchell),  in  short,  to  speak  seem- 
ingly paradoxically,  when  the  muffle  and  con- 
tents look  cold. 

An  extremely  high  heat  is  bad,  but  a  low 
heat  is  worse.  "  When  the  degree  of  heat  is 
suitable  the  cupel  is  red,  and  the  fused  metal 
very  luminous  and  clear"  (Mitchell),  and 
when  scales  of  litharge  are  found  in  small 
quantity  around  the  inner  circumference  of  the 
cupel;  in  short,  this  "feathering"  shows  that 
the  fire  has  not  been  too  hot. 


GOLD  AND   SILVER   ORES.  205 

All  this  time,  however,  the  buttons  have 
been  growing  smaller  and  smaller,  by  oxida- 
tion and  by  volatilization  and  absorption  of 
the  oxide,  changing  from  flat  liquids  to  con- 
vex ones,  and  this  reduction  continues  until 
we  reach  the  point  when  the  last  of  the  lead 
leaves  the  bead.  This  is  known  as  the 
"  brightening,"  "flashing,"  "  blicking,"  "cor- 
uscation," or  "  fuguration."  As  the  button  of 
gold,  silver,  and  lead  arrives  near  this  stage  it 
appears  to  revolve  with  great  velocity,  and 
rainbow  colors  succeed  each  other  all  over  its 
surface.  Finally  a  film  passes  over  the  bead, 
and  then  no  more  action  is  visible. 

(With  poor  silver  ores  and  ordinary  gold 
ores  the  final  bead  is  so  small  that  it  is  diffi- 
cult, if  not  impossible,  to.  see  the  "blicking," 
but  on  beads  from  silver  ores  of  any  richness 
the  brightening  shows  well  that  the  operation 
of  cupellation  is  concluded.) 

Now  move  the  cupel  to  the  hottest  place  in 
the  muffle,  or  increase  the  heat  by  closing  the 
muffle  door,  that  the  last  traces  of  lead  may 


2O6  MANUAL    OF  ASSAYING. 


be  driven  off.  One  source  of  error  in  silver 
assays  is  due  to  the  assayer  not  getting  rid  of 
all  his  lead  from  the  beads,  but  instead  he 
weighs  and  reports  it  as  silver.  Better  err  by 
under-reporting  rather  than  over,  so  take  the 
chances  of  volatilizing  a  little  silver  from  the 
bead  than  to  allow  lead  to  remain  with  the 
silver.  A  minute  is  generally  sufficient  to 
drive  off  the  last  lead,  but  with  ores  contain- 
ing more  gold  than  silver,  let  the  cupel  remain 
in  the  hot  part  three  or  four  minutes,  for 
there  is  no  danger  of  losing  any  gold  in  that 
time. 

Very  rich  ores  betray  themselves  by  a  pe- 
culiar mottled  appearance  of  the  molten  lead 
shortly  after  the  cupellation  begins.  The 
luminous  blotches  of  litharge  as  they  form 
string  themselves  out  and  cover  the  lead  as 
with  a  network.  This  is  very  characteristic, 
and  once  seen  is  again  easily  recognized. 
This  mottling  appears  also  with  almost  any 
buttons  a  little  before  the  blicking  ;  in  short, 
the  richer  the  button  the  sooner  it  is  observed. 


GOLD   'AND    SILVER   ORES.  207 

Silver  beads,  on  being  suddenly  brought 
from  the  hot  interior  of  the  muffle  to  the 
front  where  it  is  cooler,  or  out  into  the  open 
air,  sometimes  "  spit  "  or  "  blossom  " —  that  is, 
the  bead  sprouts  or  vegetates,  forming  foliated 
protuberances  all  over  its  surface.  This  may 
occasion  loss,  as  the  spitting  throws  off  parti- 
cles of  the  silver;  hence,  guard  against  this  as 
much  as  possible  by  moving  the  cupel  by  de- 
grees to  the  front,  and  when  at  the  mouth  of 
the  muffle  cover  with  an  inverted  hot  cupel. 
With  beads  weighing  less  than  30  milligrammes 
or  thereabouts  this  need  not  be  done,  but  above 
that  weight  proceed  carefully. 

If  the  assayer  is  running  a  number  of  as- 
says, let  him  so  arrange  the  cupels  that  those 
intended  for  buttons  from  poor  silver  ores  or 
gold  ores  shall  be  in  the  center  or  hottest  part 
of  the  muffle,  while  those  for  rich  silver  ores 
shall  be  in  the  fore  part  or  cooler  section. 
The  reason  for  so  doing  is  this:  silver  is  sensi- 
bly volatile  at  a  high  heat,  and  the  higher  the 
temperature  the  greater  the  loss.  On  the 


2O8  MANUAL    OF  ASSAYING. 

other  hand,  the  smaller  the  percentage  of  sil- 
ver in  a  silver-lead,  the  less  loss  of  this  metal. 
By  therefore  placing  the  rich  silver-lead  in  the 
cooler  portions,  the  tendency  is  to  decrease  the 
loss  by  volatilization.  With  any  furnace,  the 
heat  of  which  cannot  be  instantly  controlled, 
the  muffle  often  becomes  a  little  too  hot  for 
perfect  cupellation.  When  but  few  cupels  are 
therein  this  does  not  matter  much,  since  they 
can  be  slid  to  the  front;  but  it  is  of  impor- 
tance when  the  muffle  is  so  well  filled  that  it 
becomes  difficult  or  impossible  to  move  any 
particular  cupel  or  group  of  cupels  to  a  cooler 
spot.  By  now  putting  in  the  muffle  a  small 
cold  scorifier  or  cupel,  letting  it  rest  on  the 
edges  of  four  of  the  cupels,  the  interior  can 
be  cooled  down  considerably.  Several  scori- 
fiers  or  cupels  thus  arranged  have  quite  a  low- 
ering effect  on  the  temperature,  at  least  for  a 
time. 

When  many  cupels  are  being  managed  at 
once  make  a  chart  of  their  relative  positions 
in  the  muffle,  that  there  may  be  no  "  cases  of 


GOLD  AND    SILVER   ORES.  2CK) 

mistaken  identity"  afterward,  for  with  large 
buttons  in  small  cupels  the  litharge  often  ob- 
literates the  ruddle  marks. 

If  the  furnace  is  too  cold  cupellation  ceases, 
and  the  lead  button  is  said  to  "  freeze,"  form- 
ing a  bunchy  mass  which  undergoes  no  fur- 
ther action.  A  piece  of  charcoal  laid  upon 
the  cupel,  and  additional  heat  applied,  will 
sometimes  finish  the  cupellation,  or  the  but- 
ton may  be  dug  out  of  the  old  cupel,  wrapped 
in  a  piece  of  lead-foil,  and  be  re-cupelled  in  a 
new  cupel.  The  result  either  way  is  none  too 
accurate. 

The  final  silver  and  gold  bead  from  any 
cupellation  should  adhere  with  some  tenacity 
to  the  cupel,  have  a  bright,  rounded  surface, 
and  appear  frosted  below. 

d.    Weighing  the  Gold  and  Silver  Bead. 

When  cold  detach  the  bead  from  its  cupel, 
using  the  point  of  a  knife-blade,  and  keeping 
a  finger  on  the  bead  while  s'o  doing  if  the 
bead  be  small,  for  otherwise  the  exertion  put 


2  TO  MANUAL   OF  ASSAYING. 

forth  to  loosen  the  bead  might  easily  snap  it 
out  of  the  cupel  and  past  finding. 

Lift  the  bead  from  the  cupel  by  means  of 
delicate  pincers  (p.  1 18),  and  cleanse  from  any 
adhering  cupel  dirt  by  rolling  in  the  palm,  by 
using  a  small  stiff  brush,  or,  if  necessary,  by 
flattening  a  little  by  means  of  a  small  steel 
hammer  and  anvil.  If  the  bead  be  very  small, 
fold  it  in  three  or  four  thicknesses  of  tissue 
paper,  to  prevent  its  flying  away  under  the 
strokes  of  the  hammer. 

Weigh    on     the    bullion    scales     in     milli- 
grammes and  fractions. 
e.    Parting. 

The  separation  of  gold  and  silver  by  dis- 
solving out  the  latter  is  designated  by  the 
term  "parting." 

The  bead  after  weighing  is  flattened  a  little 
if  it  has  not  been  so  treated  before.  Now 
place  in  a  little  clean  porcelain  capsule  or  cru- 
cible (fig.  69),  and  fill  about  a  quarter  full 
with  water  (free  from  chlorine,  see  p.  142), 
and  add  four  to  six  drops  of  concentrated 


GOLD  AND    SIL  VER   ORES.  2  I  I 

nitric  acid.  No  exact  rule  as  to  the  amount 
of  acid  to  add  can  be  given,  nor  indeed  is  it 
necessary.  But  in  general  add  drop  by  drop 
till  it  begins  to  "bite"  the  bead  —  that  is,  when 
the  latter  seems  in  violent  motion  and  bub- 
bles are  thrown  rapidly  off.  Instead  of  add- 
ing concentrated  acid  to. water  containing  the 
bead,  until  it  takes  hold  of  the  latter,  the 
assayer  may  use  a  diluted  acid  of  known 
strength.  16  parts  of  nitric  acid  of  41°  Beaume 
(specific  gravity  1.41)  with  30  parts  of  dis- 
tilled water  will  make  an  acid  of  21°  Beaume 
(specific  gravity  1.16).  This  will  do  for  ordi- 
nary small  beads;  for  large  ones,  after  having 
treated  them  with  the  above  1.16  acid,  add 
some  of  32°  Beaume  (specific  gravity  1.26), 
made  by  mixing  16  parts  of  the  strong  41° 
acid  with  10  parts  of  distilled  water.  Make 
these  up  in  quantity  and  preserve  in  well 
stoppered  bottles. 

Now  place  the  capsule  on  a  sand-bath  or 
wire  triangle,  and  heat  gently,  not  enough  to 
cause  the  acid  solution  to  boil.  After  a  time 


212  MANUAL    OF  ASSAYING. 

no  more  action  goes  on.  If  there  is  no  gold 
in  the  bead  it  will  not  blacken  on  adding  the 
acid,  and  nothing  will  remain  undissolved  in 
the  capsule ;  it  will  contain  only  the  clear  solu- 
tion of  nitrate  of  silver,  formed  by  the  silver 
dissolving  in  the  acid. 

In  this  case  nothing  further  need  be  done 
than  to  wash  out  the  contents  of  the  capsule 
into  a  bottle  containing  silver  residues. 

But  should  one  or  more  black  specks  be 
seen  at  the  bottom  of  the  capsule  or  float- 
ing about  in  the  liquid,  gold  may  or  may  not 
be  present ;  at  all  events,  these  specks,  how- 
ever small,  must  be  treated  as  though  they 
were  gold.  Pour  off  the  liquid  above  the 
black  particles,  first  lightly  tapping  the  cap- 
sule in  order  to  cause  the  floating  gold  to 
settle  to  the  bottom.  If  tapping  will  not 
either  settle  the  gold  or  bring  the  particles 
together,  try  "churning"  -that  is,  stir  the 
contents  of  the  capsule  vigorously  with  a 
glass  rod.  In  many  cases,  and  unless  the  gold 
is  in  too  fine  a  state,  this  will  coagulate  the 


GOLD   AND    SILVER    ORES.  213 


gold,  as  it  were  —  that  is,  bring  the  particles 
together  into  a  spongy  mass  —  when  tapping 
will  quickly  settle  it.  It  is  best  to  pour  into 
another  clean  porcelain  dish,  so  that  should 
the  gold,  .by  some  mischance,  go  over  with  the 
outpouring  solution,  it  may  be  recovered.  Fill 
up  the  capsule  with  water,  care  being  taken 
that  no  speck  of  gold  is  blown  out  of  the  cap- 
sule by  the  jet  of  water  from  the  wash-bottle. 
This  is  to  wash  out  the  nitrate  of  silver  from 
the  gold.  Tap  the  gold  to  the  bottom,  pour 
off  the  washings,  and  repeat  the  washing.  If 
there  is  much  gold,  a  third  washing  may  be 
necessary.  All  this  to  insure  complete  re- 
moval of  the  silver  nitrate.  Finally  drain  off, 
wipe  the  capsule  dry,  remove,  by  means  of 
filter  paper  (or  clean  blotting  paper),  any 
drops  of  water  adhering  to  the  interior  of  the 
capsule  (being  careful  not  to  take  away  any 
of  the  gold),  and  heat  very  gently  at  first  till 
all  moisture  has  been  driven  off,  then  intensely 
for  a  minute  or  two.  The'  gold  has  now 
changed  in  color  from  black  to  its  normal  yel- 


214  MANUAL    OF  ASSAYING. 

low,  and  is  very  nearly  pure,  enough  so  for  all 
practical  purposes.      Let  the  capsule  and  con- 
tents cool. 
f.    Inquartation. 

When  a  bead  of  gold  and  silver  contains 
the  gold  in  a  greater  proportion  than  about 
one-third  of  the  silver,  it  possesses  the  power 
of  resisting  the  solvent  action  of  nitric  acid. 
A  certain  amount  of  the  silver  may  dissolve, 
according  to  the  relative  proportions  of  the 
two  metals,  but  the  larger  part  of  it  will 
remain  so  enveloped  by  the  gold,  that  the 
strongest  acid  will  not  attack  it. 

Hence  we  resort  to  inquartation,  or  the 
operation  of  producing  an  alloy  of  gold  and 
silver  in  such  proportion  that  the  latter  metal 
may  be  extracted  by  nitric  acid. 

By  the  color  of  the  bead  the  assayer  can 
judge  whether  it  needs  to  undergo  this  opera- 
tion. If  it  be  of  a  moderately  yellow  color  or 
a  brighter  yellow,  it  will  probably  need  it.  But 
there  can  be  no  doubt  of  it  if  it  refuses  to  be 
acted  upon  by  the  acid. 


GOLD   AND    SILVER   ORES.  215 

Remove  it  from  the  capsule,  and  dry. 
Weigh  some  thin  and  pure  silver  foil,  in 
quantity  about  twice  the  weight  of  the  bead. 
Wrap  the  latter  in  the  foil,  and  place  both  in 
a  cupel  (or  in  a  small  hole  bored  in  the  back 
of  the  cupel),  and  fuse  them  well  together  in 
the  flame  of  a  blow-pipe.  When  cool,  remove 
the  now  largely  increased  bead  from  the  cupel, 
flatten  and  part  as  directed. 

Instead  of  employing  the  blow-pipe,  the 
bead  and  silver  can  be  enfolded  in  some  sheet- 
lead,  and  be  re-cupelled  in  the  usual  manner. 
Indeed,  if  the  original  bead  weighs  more  than 
ten  milligrammes,  it  will  be  easier  to  alloy  it 
by  cupellation  than  by  blow-piping,  and  a 
much  better  fusion  be  obtained. 
g.  Weighing  the  Gold  Residue. 

By  means  of  a  pointed  slip  of  wood  or  sharp 
knife-blade,  transfer  the  gold  (which  should  be 
one  scale  or  film)  to  the  scale-pan  of  the  bull- 
ion balance,  and  weigh  with  exceeding  care,  as 
usual  in  milligrammes  and  fractions.  It  often 
happens  that  the  minute  black  pin-point  of 


2l6  MANUAL    OF  ASSAYING. 

gold  becomes   too  small  to  be  weighed  after 
the  heating.      It  can  then  be  reported  only  as 
a  "trace"  or  "color." 
h.    Calculations. 

By  the  use  of  the  system  of  assay  ton 
weights,  the  calculation  of  the  gold  and  silver 
value  of  an  ore  becomes  very  simple.  Two 
examples  will  show  this  very  clearly  : 

EXAMPLE  No.   i. 

Amount  of  ore  taken \  A.  T. 

Amount  of  test-lead  used i \     " 

MGRMS. 

Weight  of  gold  and  silver  bead 8.50 

silver  in  i£  A.  T.  lead 25 

True  weight  of  gold  and  silver  bead 8.25 

Weight  of  gold  in  the  bead i.io 

Weight  of  silver  in  the  bead 7.15 

7.15  X  5  =  35-75  =  35i  milligrammes  =  35! 
ounces  per  ton  of  silver  in  the  ore. 

1.10x5  =  5.5  =  5^  milligrammes  =  5^  ounces 
per  ton  of  gold  in  the  ore. 

VALUE    OF    THE    ORE! 

Gold — 5^  ounces  @  $20.67  per  oz $113.68 

Silver— 35f     "       "        1.29       "       46.11 

Total  value  per  ton $159.79 


GOLD   AND   SILVER    ORES.  217 

EXAMPLE  No.  2. 

Amount  of  ore  taken \  A.  T. 

Amount  of  test-lead  used i       " 

MGRMS. 

Weight  of  gold  and  silver  bead 231.90 

Weight  of  silver  in  test-lead* o.oo 

True  weight  of  gold  and  silver  bead 231.90 

Weight  of  gold,  "  faint  trace  " o.oo 

Weigh  of  silver  in  the  bead 231.90 

23 1.9x2  =463.8=463^  milligrammes=4631%- 
otmces  per  ton  of  silver  in  the  ore. 

Value  :  463-8 x  $1*29  =$59 7.^0  per  ton. 

CRUCIBLE     PROCESS. 

This  process  is  much  more  complicated 
than  the  scorification,  and,  to  use  it  success- 
fully, we  should  know  pretty  thoroughly  the 
nature  of  the  re-agents  employed,  the  kind 
and  degree  of  their  re-actions  upon  each  other 
and  upon  the  ore  while  in  the  crucible  sub- 
jected to  heat,  and,  finally,  the  characters  of 
the  various  ores  and  their  modes  of  behavior 

*  Not  deducted.  Read  remarks  on  testing  of  granulated  lead 
for  silver,  p.  159. 


2l8  MANUAL    OF  ASSAYING. 

in  the  crucible.  Knowing  all  these  things, 
we  can  decide  upon  such  a  modification  of 
treatment  as  is  best  adapted  to  the  particular 
ore  in  question. 

The  crucible  process  can  be  applied  to  any 
gold  and  silver  ore,  of  whatever  mineralogical 
nature,  and  whether  rich  or  poor,  but  it  has 
been  found  by  experience  to  be  best  fitted  for 
certain  ores  and  classes,  as  is  the  scorification 
for  certain  others. 

By  some  assayers  the  crucible  process  is 
reserved  almost  entirely  for  low  grade  ores 
(whether  in  gold  or  silver),  and  the  scorifica- 
tion  for  high  grade  ores,  and,  for  a  general 
rule,  this  will  do  very  well.  Another  broad 
distinction  is  that  of  confining  the  crucible 
process  to  gold  ores,  and  the  scorification  to 
ores  of  silver.  This  latter  rule  is  quite  a  safe 
one  to  follow,  since  the  majority  of  gold-bear- 
ing ore  is  low  grade,  and  hence  is  best  assayed 
by  the  crucible  process,  which  operates  upon 
a  larger  quantity  than  the  scorification.  Fur- 
ther, an  ore  of  silver  which  is  so  poor  as  to 


GOLD  AND   SILVER   ORES. 


2I9 


give  no  results  by  the  scorification  process,  is 
practically  worthless,  and  needs  no  more  test- 
ing by  any  method. 

The  following  classification  covers  the 
ground,  both  generally  and,  in  a  measure,  spe- 
cifically: 


CRUCIBLE   PROCESS. 

1.  Gold  ores. 

2.  Low  grade  gold  ores.* 

3.  Low  grade  silver  ores. 

4.  "  Chloride    ores  "    (sil- 

ver), including: 
"  Chlorides, 
Bromides, 
Chloro-bromides, 
Iodides. 


SCORIFICATION    PROCESS. 

1.  Silver  ores. 

2.  High  grade  silver  ores, 

with  the  exception  of 
the  chloride  and  al- 
lied ores. 

3.  High  grade  gold  ores. 

4.  Telluride  ores. 

5.  Arsenical  and   antimo- 

nial  ores. 

6.  Ores  containing  tin. 

7.  Ores  containing  nickel 

or  cobalt. 

An  outline  of  the  crucible  process  is  as 
follows  : 

The  ore  is  mixed  «with  lead  in  some  form, 

*  For  the  purposes  of  assaying,  a  gold  ore  which  runs  over  $5 
to  the  ton  may  be  considered  high  grade  ;  below  that  figure,  low 
grade. 


22O  MANUAL   OF  ASSAYING. 

fluxes,  with  or  without  some  reducing,  oxidiz- 
ing, sulphurizing,  or  desulphurizing  agent, 
transferred  to  a  crucible  and  heated.  The 
reduced  lead  absorbs  the  gold  and  silver,  and 
settles  with  them  to  the  bottom,  while  all  im- 
purities are  fluxed  (i.e.,  slagged),  matted,  or 
volatilized.  After  removal  from  fire  the  lead 
is  freed  from  slag,  and  the  gold  and  silver 
separated  from  it  by  cupellation,  as  previously 
described. 

To  elaborate  the  above  description  some- 
what, we  may  state,  that,  in  the  crucible  pro- 
cess, as  in  the  scorification,  lead  is  added 
(save  for  lead  ores)  to  extract  the  precious 
metals  from  the  ore  ;  but,  instead  of  using  it 
in  the  metallic  state  and  oxidizing  the  excess, 
we  start  with  a  compound  which  is  almost  in- 
variably the  oxide,  litharge,  and  by  means  of 
a  reducing  agent,  or  by  the  reducing  action  of 
the  ore  itself  (or  by  both  combined),  reduce 
enough  lead  to  retain  all  the  gold  and  silver, 
but  which  amount  of  lead  shall  not  be  too 
large  to  be  manageable. 


GOLD  AND   SILVER   ORES.  221 

To  secure  a  perfect  crucible  fusion,  which 
means  practically  the  separation  of  the  gold 
and  silver  from  everything  else  that  may  have 
been  associated  or  combined  with  them  in  the 
ore  (excepting,  perhaps,  some  of  the  lead), 
we  need  to  do  several  things.  To  get  rid  of 
the  gangue  (or  earthy  portion  of  the  ore)  we 
use  fluxes,  which  convert  the  gangue  into  a 
slag.  All  metals  present,  save  the  precious 
ones,  may  be  removed  in  various  ways  :  By 
uniting  them  with  sulphur  into  a  matte  ;  by 
oxidizing  them  and  fluxing  the  oxides  into  the 
slag  ;  by  oxidizing  them  and  volatilizing  the 
oxides  entirely  out  of  the  crucible  ;  or,  in  the 
one  case  of  lead,  by  bringing  either  the  whole, 
or  such  a  proportion  of  it  as  may  be  wanted, 
down  with  that  obtained  from  the  litharge. 
Next,  we  may  or  may  not  need  some  reducing 
agent  to  reduce  the  requisite  amount  of  lead  ; 
or,  on  the  contrary,  a/i  oxidizing  agent  may  be 
necessary  to  oxidize  and  so  remove  sulphur  or 
the  excess  of  lead  when  an  ore  of  this  metal 
is  being  treated.  Finally,  a  protecting  cover 


222  MANUAL   OF  ASSAYING. 


of  some  easily  fused  inert  substance  will  be 
wanted,  although  it  is  not  indispensable. 

The  chief  fluxes  are  litharge,  the  carbon- 
ates and  bi-carbonates  of  potash  and  soda, 
borax,  silica,  and  nitre.  The  reducing  agents 
are  charcoal,  argol,  cream  of  tartar,  flour,  or 
some  other  similarly  carbonaceous  substance, 
for  it  is  the  carbon  of  the  reducing  agent 
which  removes  the  oxygen  of  the  litharge, 
leaving  metallic  lead.  The  most  commonly 
used  oxidizing  agent  is  nitre.  Sulphur  is  the 
sulphurizing  agent,  and  common  salt  the  pro- 
tecting cover.  (The  chemical  composition 
• 

and  reactions  of  all  the  above  are  given  in 
detail  in  the  chapter  on  re-agents,  which  see.) 
It  will  now  be  well,  and  in  order,  to  under- 
take a  little  study  of  gold  and  silver  ores,  or 
of  ores  which  are  imagined  to  contain  the 
precious  metals,  that  we  may  know  how  to 
apply  to  them  their  proper  treatment,  which 
includes  a  knowledge  of  the  principles  of  the 
important  art  of  fluxing. 


GOLD  AND    SILVER   ORES. 


223 


Every  ore  must  belong  in  some  one  of  the 
following  divisions  : 


Metalliferous    min- 

Gangue matter  with 

eral    or    minerals 

no  perceptible  met- 

with    a    gangue  ; 

alliferous  mineral 

examples,   galena 

or  minerals;    ex- 

or iron  pyrites  in 

amples,  quartz, 

quartz. 

fluor  spar  or  ba- 

rytes. 

Metalliferous  min- 
eral or  minerals 
with  no  gangue; 
examples,  pure 
galena,  iron  py- 
rites, or  any  "con- 
centrates." 


The  third  division  can,  of  course,  include 
specimens  that  actually  contain  no  metallifer- 
ous minerals,  perceptible  or  imperceptible,  as, 
for  example,  pure  white  quartz,  while  in 
others,  as  stated,  they  may  be  present  so  mi- 
nutely disseminated  as  to  be  invisible  to  the 
naked  eye  (or  even  to  the  eye  assisted  by  a 
good  magnifying  glass),  as  is  often  true  of 
samples  carrying  gold  in  that  very  fine  condi- 
tion known  as  "  flour  gold." 

There  are  also  instances  where  that  which 
is' ordinarily  a  metalliferous  mineral  may  act 
as  a  gangue  ;  for  example,  galena  in  spathic 
iron.  Here  the  latter  is  a  gatngue,  whereas 
at  other  times  it  may  be  found  as  a  mineral 


224  MANUAL   OF  ASSAYING. 


in  a  true  gangue.  No  confusion,  however, 
need  arise,  if  we  consider  only  the  question 
of  the  composition  of  the  particular  sample 
lying  before  us. 

The.  chief  value  of  the  above  classification 
lies  in  the  fact  that  a  knowledge  of  the  class 
to  which  an  ore  belongs  aids  us  in  its  fluxing. 

It  would  be  almost  impossible  to  write  such 
descriptions  as  would  enable  the  student  to 
determine  the  mineralogical  character  of  an 
ore  or  to  place  it  in  its  proper  division  above. 
He  must  learn  by  experience,  by  observation, 
and  by  an  application  of  the  information  im- 
parted by  the  standard  authorities  on  miner- 
alogy and  blow-pipe  analysis  which  are  listed 
in  the  appendix.  The  few  simple  qualitative 
tests  given  in  the  latter  may  aid  him  some- 
what. 

As  regards  the  relative  amounts  of  gancrue 

o  o         & 

and  mineral  in  an  ore,  I  can  give  but  one  gen- 
eral, and  rather  indefinite,  line  of  advice  : 
The  heavier  an  ore,  the  greater  the  percent- 
age of  metalliferous  mineral ;  the  lighter  an 


GOLD  AND   SILVER   ORES.  22$ 

ore,  the  greater  the  percentage  of  gangue. 
There  are  a  few  exceptions  to  this  rule  ;  the 
chief  one  commonly  met  with  is  barytes  or 
heavy  spar,  a  gangue  which  is  three-fifths  as 
heavy  as  galena,  the  chief  ore  of  lead. 

If  an  ore  to  be  treated  belongs  to  the  first 
division  —  that  is,  if  it  possesses  no  gangue  — 
we  supply  an  artificial  one,  as  it  were,  when 
we  come  to  prepare  the  charge,  by  adding 
silica. 

For  purposes  of  assay  treatment,  we  may 
consider  under  one  heading  those  ores  which 
appear  to  be  all  gangue,  or  made  up  of  both 
gangue  and  mineral. 

The  nature  of  the  gangue  is  important  in 
determining  the  nature  of  the  flux  necessary 
to  change  it  all  into  a  slag.  The  gangue  may 
be  acid,  basic,  or  both  acid  and  basic ;  conse- 
quently, the  simple  rules  for  fluxing  a  gangue 
are  almost  self-evident.  An  acid  gangue  re- 
qiures  a  basic  flux  /  a  basic  gangue  requires 
an  acid  flux.  Now,  what  do  we  mean  by  an 
acid  or  a  basic  gangue  ?  An  acid  gangue  is 


226  MANUAL    OF  A SSA  YING. 

simply  one  which  acts  as  an  acid,  requiring  a 
base  to  form  a  salt.  A  basic  gangue,  on  the 
contrary,  acts  as  a  base,  and  therefore  requires 
an  acid  to  form  a  salt.  As  examples  of  these 
chemical  facts,  take  metallic  copper,  which  is 
a  base.  To  convert  it  into  a  salt  of  copper 
we  need  an  acid,  which  may  be  sulphuric,  this 
making  sulphate  of  copper  (common  blue 
vitriol),  or  silicic  acid,  forming  silicate  of  cop- 
per (the  mineral  chrysocolla  is  the  hydrated 
silicate  of  copper),  or  any  other  acids,  form- 
i,ng  corresponding  salts.  So  in  fluxing,  an 
acid  gangue,  as  silica,  forms  salts  with  a  basic 
flux,  as  litharge  or  soda,  producing  a  slag 
which  is  composed  of  the  silicates  of  lead  and 
soda,  and  a  basic  gangue,  as  lime,  unites  with 
acid  fluxes,  as  silica  or  borax,  producing  a 
slag  which  is  composed  of  the  silicate  and 
borate  of  lime.  There  results  then  the  fol- 
lowing classification  : 


GOLD  AND    SILVER   ORES. 


227 


ACID    GANGUES. 

1.  Quartz,  or  other  forms 

of  uncombined  silica ; 
as  quartz  crystals, 
quartz  rock,  quartz- 
ite,  sandstone,  sand, 
etc. 

2.  Silicates,  or  silica  com- 

bined with  some  base; 
as  clay,  clay  slates, 
mica,  etc. 

3.  Rocks   in   which   silica 

predominates;  as  gran- 
ites, feldspars,  por- 
phyry, etc. 

As  a  rule,  then,  an  acid 
gangue  is  silicious. 


BASIC    GANGUES. 

1.  Calc  spar  (carbonate  of 

lime).  Also  lime- 
stones. 

2.  Heavy  spar  (barytes,  or 

sulphate  of  baryta). 

3.  Fluor  spar  (fluoride  of 

calcium). 

4.  All  so-called  earths;  as 

alumina,  and  various 
combinations  of  lime, 
magnesia,  baryta, 
etc.,  without  silica. 

5.  Sparry  iron,  or  carbon- 

ate of  iron. 

6.  Various    metallic    ox- 

ides; as  those  of  iron, 
manganese,  etc., 
when  in  sufficient 
quantity  to  be  con- 
sidered as  gangues. 


We  can  easily  see  now  that  the  gangue  of 
an  ore  may  be  both  acid  and  basic,  by  its  being 
made  up  of  representatives  o'f  both  classes. 
Theoretically,  then,  such  a  gangue  should 


228 


MANUAL  OF  ASS  A  YING. 


flux  itself.      Practically,  however,  we  may  find 
it  necessary  to  help  the  fusion  a  little. 

Try  to  ascertain  the  mineralogical  character 
of  the  gangue.  When  this  is  known,  con- 
sider only  the  element  which  is  in  excess  of 
the  others,  and  flux  that ;  the  remaining  ones 
will  usually  take  care  of  themselves. 


ACID  FLUXES. 

1.  Borax. 

2.  Silica. 

3.  Silicates  ;  as  glass,  and 

silicate  of  lead  or 
lead-glass  formed  by 
the  fusion  of  litharge 
and  silica. 

Hence  these  flux  the 
basic  gangues  enumer- 
ated. 


BASIC  FLUXES. 

1.  Litharge. 

2.  Nitre. 

3.  Carbonate  of  soda. 
Carbonate  of  potash. 
Bicarbonate  of  soda. 
Bicarbonate  of  potash. 


Hence  these  flux  the 
acid  gangues  enumer- 
ated. 

The  metalliferous  minerals  of  an  ore  play 
a  very  important  part  in  its  treatment.  T^hey 
may  exert  either  one  of  two  very  opposing 
actions,  viz.:  reducing,  that  is,  taking  away 
oxygen  (from  the  litharge),  or  oxidizing,  that 
is,  giving  up  oxygen  (to  the  reducing  agent). 


GOLD  AND   SILVER   ORES.  22Q 


To  explain  a  little  more  fully:  Sulphur, 
arsenic,  antimony,  and  zinc  are  the  principal 
reducing  elements  of  an  ore.  (If  an  ore  con- 
tains none  of  these,  it  will  not  be  at  all  reduc- 
ing.) They  all  act  in  a  similar  manner  to  the 
carbon  of  a  reducing  agent,  removing  oxygen 
from  the  litharge,  and  so  leaving  metallic  lead, 
themselves  being  converted  into  oxides.  The 
various  methods  for  eliminating  these  obnox- 
ious substances  will  be  considered  further 
along. 

An  effect  contrary  to  that  produced  by  the 
elements  mentioned  is  that  caused  by  certain 
oxides  and  oxidized  minerals.  They  are 
chiefly  the  oxides  of  iron,  lead,  copper,  and 
manganese,  in  their  highest  forms  of  oxida- 
tion. Exposed  to  heat  in  a  crucible,  and  sur- 
rounded by  the  reducing  agent,  they  give  up 
to  it  a  portion  of  their  oxygen,  themselves 
being  converted  into  their  lower  oxides  and 
going  into  the  slag. 

The  presence,  then,  of  either  reducing  or 
oxidizing  elements  in  an  ore  is  made  manifest 


230  MANUAL    OF  A SSA  YING. 


by  the  size  of  the  resulting  lead  button,  the 
former  tending  to  produce  lead,  the  latter  to 
keep  it  in  the  oxidized  state  by  appropriating 
to  themselves  the  carbon  intended  for  reduc- 
ing. Thus,  some  ores  will  be  more  or  less 
reducing,  bringing  down  more  lead  than  is 
wanted,  just  enough  or  too  little,  or  they  may 
reduce  no  lead  at  all.  On  the  other  hand, 
they  may  be  oxidizing,  not  only  not  bringing 
down  any  lead,  but  preventing  the  reducing 
elements  of  the  ore  (if  present)  and  the  re- 
ducing agent  added  from  exerting  their  action. 
Hence  it  is  important  to  know  what  an  ore's 
action  is. 

It  is  advisable  to  reduce  a  certain  portion 
of  the  litharofe  in  order  to  obtain  a  button  of 

£5 

a  convenient  size  for  cupellation.  It  should 
be  large  enough  to  extract  all  the  gold  and 
silver  from  the  ore,  yet  not  be  so  large  as  to 
be  too  long  time  cupelling,  which  may  cause 
a  loss  in  silver.  A  standard  weight  is  15 
grammes  for  those  who  use  the  metric  sys- 
tem, or  240  grains  (^  ounce)  for  those  accus- 


GOLD  AND   SILVER   ORES. 


tomed  to  the  grain  weights.  If  the  buttons 
obtained  should  chance  to  be  somewhat  larger 
or  smaller,  it  will  make  no  material  difference; 
but  it  is  well  to  use  either  weight  given,  and 
calculate  ores  and  oxidizing  and  reducing 
agents  to  such  a  basis. 

For  the  sake  of  reference,  I  next  give  lists 
of  the  principal  ores  and  minerals  whose  direct 
or  indirect  action  upon  the  litharge  has  just 
been  discussed. 

Metalliferous  minerals  which  have  a  rediic- 
ing  action  : 

SULPHURETS. 

1.  Sulphuret  of  zinc  (sphalerite,  blende,  zinc 

blende,  "jack"  or  "black  jack"). 

2.  Sulphuret  of  manganese  (manganblende, 

alabandite). 

3.  Sulphuret  of    iron   (pyrite,  iron  pyrites, 

mundic). 

4.  Sulphuret  of   iron  (pyrrhotite,  magnetic 

iron  pyrites). 

5.  Sulphuret  of  iron  with  arsenic  (arsenopy- 

rite,  mispickel,  arsenical  iron  pyrites). 


232  MANUAL    OF  A SSA  YING. 

6.  Sulphuret  of  copper  (chalcocite,  copper 

glance,  vitreous  copper). 

7.  Sulphuret  of  copper  and  iron  (chalcopy- 

rite,  copper  pyrites). 

8.  Sulphuret    of  copper  and  iron  (bornite, 

erubescite,  variegated  copper  pyrites, 
"  horse-flesh  ore  "). 

9.  Sulphuret  of  copper  and  antimony  with 

sulphurets  of  iron,  zinc,  silver,  mercury, 
bismuth,  arsenic,  etc.  (tetrahedrite,  gray 
copper,  fahlerz). 

10.  Sulphuret  of  antimony  (stibnite,  gray  an- 

timony). 

11.  Sulphuret  of  lead  (galenite,  galena,  "  py- 

rites of  lead,"  "  mineral  •). 

12.  Sulphuret    of     silver     (argentite,    silver 

glance). 

The  above  list  enumerates  the  chief  sul- 
phurets which  are  likely  to  be  assayed  for 
gold  and  silver,  though  there  are  many  other 
intermediate  and  mixed  sulphurets,  for  de- 
scriptions of  which  consult  the  mineralogies. 
It  can  easily  be  remembered,  however,  that 


GOLD   AND   SILVER   ORES.  233 

any  sulphuret,  or  mixture  of  sulphurets,  is 
reducing. 

To  the  above  add  the  various  arsenides, 
antimonides,  bismuthides,  selenides,  etc.,  of 
more  or  less  rarity,  and  more  commonly  ores 
containing  graphite  or  plumbago. 

Metalliferous  minerals  which  have  an  oxid- 
izing action  : 

1.  Red    oxide    of    iron    ("  decomposed    iron 

ore  "). 

2.  Red  oxide  of  lead  (minium). 

3.  Black  oxide  of  copper  (tenorite,  melaco- 

nite). 

4.  Black  oxide  of  manganese  (pyrolusite). 

(More  rarely  the  chromates). 

Since  an  oxidized  ore  commonly  results 
from  the  decomposition  of  a  sulphuretted 
one,  it  may  be  very  possible  to  find  an  ore 
not  entirely  decomposed  or  oxidized,  and 
therefore  both  reducing  and  oxidizing.  As 
examples,  one  often  meets  with  a  specimen 
carrying  sulphurets  and  oxides  of  iron,  or 


234  MANUAL   OF  ASS  A  YING. 

copper  pyrites  and  black  oxide  of  copper  in- 
termingled, or  galena  and  carbonate  of  lead. 

A  preliminary  examination  of  an  ore  may 
then  be  necessary  to  determine  its  character 
and  subsequent  mode  of  treatment.  An  ex- 
pert mineralogist,  metallurgist,  miner,  or  as- 
sayer  can  tell  almost  at  a  single  glance  the 
nature  of  an  ore  as  to  its  constituents  and 
oxidizing  or  reducing  powers,  but  the  begin- 
ner will  find  it  somewhat  difficult  at  first. 
Here  then  again  comes  in  the  opportunity  to 
make  blow-pipe  and  qualitative  examinations. 

To  ascertain  the  presence  or  absence  of 
sulphurets,  try  the  following  very  simple  test: 
Powder  a  little  of  the  sample  and  heat  it  in 
an  iron  spoon  over  a  strong  flame  or  on  top 
of  a  good  fire,  and  note  its  behavior.  If, 
shortly  after  it  is  heated,  star-like  sparks  are 
quickly  thrown  off  (particularly  noticeable 
when  the  powder  is  stirred  with  a  wire),  then 
the  mass  begins  to  glow  around  the  edges 
(resembling  a  charcoal  fire),  while  closely 
above  it  hover  small  blue  flames,  and  finally 


GOLD  AND   SILVER   ORES.  235 

the  entire  mass  becomes  red-hot,  with  fumes 
and  an  odor  as  of  a  burning  match  is  per- 
ceived, then  sulphurets  of  iron  or  copper  or 
both  are  present,  and  so  the  ore  will  be  decid- 
edly reducing.  If,  in  addition,  an  onion  or 
garlic-like  odor  and  whitish  fumes  are  noticed, 
arsenic  (probably  as  arsenical  iron  pyrites) 
is  also  present.  Antimony  and  zinc  give  white 
fumes  with  no  odors.  Blende  and  galena  are 
not  so  liable  to  glow  and  to  scintillate  as  are 
the  iron  and"  copper  sulphurets,  but  the  smell 
of  a  burning  match  should  be  perceptible  upon 
heating  them  or  any  other  ore  which  contains 
a  fairly  large  percentage  of  sulphurets.  It 
will  also  be  noticed  that  after  the  mass  has 
been  thoroughly  heated  and  allowed  to  cool, 
it  will  have  lost  its  metallic  shimmer,  and  be- 
come of  a  dull,  dead  color,  indicating  oxida- 
tion. 

A  simple  chemical  test  for  sulphurets  may 
easily  and  quickly  be  tried.  Place  a  small 
portion  of  the  finely  ground  Ore  in  a  test- 
tube,  pour  in  a  little  water,  shake,  add  a  few 


236  MA  NUAL   OF  ASS  A  YING. 

drops  of  hydrochloric  acid,  and  warm  gently. 
If  the  smell  peculiar  to  rotten  eggs  (sulphu- 
retted hydrogen)  is  now  recognizable,  sulphu- 
rets  are  certainly  in  the  ore. 

Finally,  when  it  is  suspected  that  not  a  very 
large  quantity  of  any  sulphuret  is  in  the  sam- 
ple, try  the  following  plan,  which  is  much  more 
delicate  than  either  of  the  preceding  :  Fuse  a 
little  of  the  ore  with  bicarbonate  of  soda  and 
borax  on  charcoal,  by  means  of  the  blow-pipe. 
When  the  mass  has  fused  remove  it,  by  means 
of  a  knife-blade,  to  the  surface  of  a  bright 
silver  coin,  add  a  drop  of  water,  and  work  the 
paste  thus  formed  for  a  short  time.  The  same 
gas  above  spoken  of  (sulphuretted  hydrogen) 
is  given  off  from  the  sulphide  of  sodium, 
which  has  been  made  by  the  union  of  the  sul- 
phur of  the  ore  and  the  soda,  and  blackens 
or  browns  the  coin,  according  to  the  amount 
of  sulphur  in  the  original  ore. 

•  A  very  close  guess  as  to  the  kind  of  sul- 
phuret contained  in  an  ore,  or  of  which  it  is 
mostly  composed,  can  frequently  be  made  (de- 


GOLD  AND   SILVER   ORES.  237 

pending  on  the  purity  of  the  sulphuret)  by 
noting  the  color  and  character  of  the  pulver- 
ized sample,  then  heating  some  quickly  in  a 
roasting  dish,  observing  its  action  under  heat, 
finally  examining  the  heated  ore,  after  it  has 
cooled.  Compare  it  with  the  following  table  : 


238 


MANUAL   OF  ASSAYING. 


KIND  OF  SULPHUKET. 

BEFORE  HEATING. 

DURINC- 

Color  of  Ore. 

Character. 

Fumes. 

Character. 

I. 

2. 

3- 
4- 

5- 
6. 
7- 
8. 

9- 

10. 

ii. 

12. 

Blende  

Manganblende  .  . 
Pyrite...    . 

(  Brown,  shading  \ 
•<      to  green,  red,  > 
/      and  yellow.      ) 

)  Green,     green-  ( 
1      ish-gray.           f 

(Greenish    or  i 
•<      brownish     > 
1      black.                j 

Gray-black  

« 
Gray-black  

Shining  

Dull  

{Shining,  not  ( 
"/      magnetic.         f 

(Shining,     is  I 
|      magnetic.         ) 

Shining  

Very  slight  
Slight  

Slight  
Slight 

Pyrrhotite  .  . 
Arsenopyrite  
Chalcocite  
Chalcopyrite 
Bornite  
Tetrahedrite  

Stibnite  
Galenite 

(  White,  very  > 

')      thick.          f 

Slight 

Green-black  
Dark-green    
Dark-gray  

Lead-gray  

Gray  

(  Gray  -  black,  J 
-c      pink      and> 
f     brown  shades,  j 

Shining  
Shining        .   .  . 

Some  fumes  
Some  fumes  
Much  

White  fumes.  .  . 

(  Fumes  con-  .' 
"/      siderably.  )" 

Some  

Shining                 .  . 

Shining  
Very  decided  shine. 
Very  little  shine  .  .  . 

Argentite  ...  — 

(Each  sulphuret  will  give  a  little  odor  of  sulphur,  but 


GOLD  AND   SILVER   ORES. 


239 


HEATING. 

AFTER  HEATING  (WHEN  COLD). 

Fumes. 

Other    Char- 
acteristics. 

Color  of  Ore. 

Character. 

Composition. 

Odor. 

None  

fGlows,! 
i     yellow- 
-j      green}- 
whe  n  1 
I     hot.        J 

j  Buff  or  yel-  j 
1      lowish.       f 

Dead,  dull  .... 

Oxide  of  zinc. 

None  

Glows.  ...... 

Brown  .  .   

Dead,  dull  

j  Brown    oxide 
|  ofmanganese. 

None  

Glows  

(  Red  to  black  ) 
•<      —  m  any    V 
(     shades.       \ 

Dead,  dull  

|  Red   oxide  of 
|     iron. 

None  

Glows  

(  Red  to  black  ) 
<     —  man  y  V 
(     shades.       \ 

Dead,  dull  

j  Red   oxide  of 
/      iron. 

Like  garlic  

(  Glows,  | 
"/      swells.   1 

(  Red  to  black  ) 
-<      —  m  any  V 
(      shades.       ) 

Dead,  dull.... 

(  Red  oxide  of 
(      iron. 

None  

Glows,  fuses. 

Gray  

1  Shining,  ) 
<     powdefV 
(      red.             \ 

i  Oxide  of  cop- 
"/      per. 

None  .  . 

Glows,  fuses 

Gray  

(  Shining,  1 
•<      powderV 
(     gray.          ) 

(  Oxides  of  iron 
"(      and  copper. 

None  

Glows  

Gray  

(Shining,  1 
•<      powderV 
(      brown.       \ 

j  Oxides  of  iron 
1     and  copper. 

(  Garlic  odor  ) 
A      some-         > 
f         times.      ) 

(Glows,    ) 
<     swells,  V 
\     fuses.     | 

Gray  

Shining 

Mixed  oxides. 

None  

(Swells,    ) 
<     melts,     V 
(      boils,      i 

Gray-green 

(  A  thin   film  1 
•C      of  shining  > 
(      mass.          j 

j  Oxide  of  anti- 
j      mony. 

None  

Fuses  

Yellow-green  .  . 

Shining  

Oxide  of  lead. 

None  

Fuses  

Gray  

J  Somewhat     > 
I     shining,      f 

(  Oxide  of  silver 
-<     s  o  m  e  w  hat 
f     reduced. 

it  is  not  to  be  confounded  with  the  odor  of  arsenic.) 


240  MANUAL    OF  ASSAYING. 

An  approximate  determination  of  the  per- 
centage of  "  sulphurets "  in  an  ore  can  be 
made  by  mixing  10  grammes  or  100  grains  of 
the  ore  with  as  much  powdered  silica  and 
twice  as  much  borax  glass,  placing  the  mix- 
ture in  a  suitably  sized  crucible,  topping  with 
salt,  covering,  and  heating  pretty  strongly  for 
fifteen  minutes.  Remove,  cool,  break  out 
button  as  a  "  matte,"  weigh,  and  multiply 
weight  by  ten,  giving  percentage. 

The  blow-pipe  tests  for  antimony  and  zinc 
are  not  satisfactory,  especially  in  the  hands  of 
a  beginner;  hence,  I  have  given  the  following 
analytical  scheme,  which,  although  it  seems 
complicated,  is  really  simple.  It  can  be  ap- 
plied to  the  most  complex  ores;  for  the  more 
simple  ones  some  of  the  steps  can  be  omitted, 
as  the  student  will  learn  by  experimenting  with 
it  on  the  various  ores  and  minerals.  To  prac- 
tice it,  make  a  mixture  of  iron  and  copper  py- 
rites, blende,  galena,  arsenopyrite,  sulphuret  of 
antimony,  and  black  oxide  of  manganese.  The 
test  can  be  made  in  an  hour's  time. 


GOLD   AND    SILVER   ORES. 


241 


Make  a  mixture,  in  equal  parts,  of  hydro- 
chloric, nitric  and  sulphuric  acids.  Place  this 
in  a  beaker,  and  into  it  drop  some  of  the 
powdered  ore,  and  heat ;  then  add  water,  and 
filter.  Do  not  wash. 


Residue  and  Precipitates. 
Sand,  silica,  clay;  mercury,  silver, 
and  lead  as  chlorides;  lead,  calcium, 
barium,  and  strontium  as  sulphates; 
antimony  as  oxychloride.   Wash  thor- 
oughly with  water  while  on  the  filter. 

Filtrate. 
Add    sulphuretted    hydrogen   gas, 
and  filter  from  precipitate  formed. 

Precipitate. 
Mixture    of 
various 
sul  phu- 
rets  ;    r  e  - 
ject. 

Filtrate. 
Boil  off  excess  of  sul- 
phuretted hydrogen, 
add  caustic  soda  in  ex- 
cess, boil  and  filter. 

Filtrate. 
Not  needed, 
reject. 

Res.  and  Pre. 
Remove    from    filter, 
boil    with    solution    of 
,  and  filter. 

tartaric  acid 

Precipitate. 
Iron,    chro- 
mium, al- 
uminium, 
and  man- 
ganese as 
hydra  ted 
sesqui  o  x- 
ides. 

Filtrate. 
Add    acetic    acid    in 
excess,  and  treat  with 
sulphuretted  hydrogen; 
a  white  precipitate  in- 
dicates the  presence  of 
zinc. 

Res. 
As      first 
given;  re- 
ject. 

Filtrate. 
Run  sulphuretted  hy- 
drogen gas  through  it, 
or  add  water  saturated 

with  this  gas;  an  orange-colored  pre- 
cipitate indicates  antimony. 

It  is  difficult  to  give  tests  for  the  highly 
oxidized  ores  listed.  Dull,  dead  ores  in  gen- 
eral are  likely  to  be  in  an  oxidized  condition, 
though  not  necessarily  in  the  highest  state  of 
oxidation.  If  the  ore  is  red  and  does  not 


242  MANUAL    OF  ASSAYING. 

answer  to  any  test  for  copper,  it  will  proba- 
bly be  the  red  oxide  of  iron  (possibly  of  lead). 
If  it  is  black,  apply  the  simple  tests  for  cop- 
per and  manganese  given  in  the  appendix. 

But  even  without  a  knowledge  of  the  ore, 
gained  by  observation  and  experience,  or  by 
applying  tests,  its  reducing  or  oxidizing  power 
can  be  determined  by  certain  preliminary  and 
arbitrary  assays. 

If  it  is  suspected  th^t  the  ore  is  reducing, 
prepare  the  following 

PRELIMINARY  CHARGE   TO    DETERMINE   REDUCING   POWER. 

A.   7\   Weights*  Gramme  Weights*  Grain  Weights.* 

Litharge  .  . .  ij  A.T.  45  grammes  720  grains. 

Ore ^    «  14          "  24       « 

Salt  cover. 

(The  above  weights  of  ores  are  each  -fa  of 
the  respective  standard  weights  taken  for  the 
crucible  process.) 

Weigh  first  the  litharge  and  brush  it  on  to 

*  These  weights  do  not  correspond  exactly  with  one  another 
(although  sufficiently  so),  nor  is  it  demanded  that  they  should.  They 
simply  represent  the  most  appropriate  quantities  for  the  purpose  in 
the  several  systems  of  weights.  The  student  can  take  his  choice. 


GOLD   AND    SILVER   ORES.  243 


a  clean  sheet  of  black  glazed  paper,  then 
weigh  very  carefully  the  finely  pulverized  ore, 
sampling  it  as  usual;  brush  it  on  top  of  the 
litharge,  and  mix  them  thoroughly  (indicated 
by  the  uniform  color  and  character  of  the  re- 
sulting compound)  with  a  large  steel  spatula. 
Pour  the  charge  into  a  small  sand  crucible, 
which  it  should  not  more  than  two-thirds  fill 
(size  "  W "  of  the  Battersea  make,  3  inches 
deep  by  2\  inches  across,  will  do  nicely)  ;  tap 
gently  till  contents  are  level,  sprinkle  some 
dry  salt  over  the  glazed  paper,  stir  it  around 
thereon  by  half  turning  over  the  sides  of  the 
paper,  finally  pour  it  on  top  of  the  charge - 
in  this  manner  any  of  the  charge  left  adher- 
ing to  the  paper  is  "  dry  washed  "  into  the  cru- 
cible. There  should  be  about  \  inch  salt  on 
top.  There  will  then  remain  an  inch  or  so 
space  between  top  of  crucible  and  the  salt,  to 
allow  for  the  expansion  of  the  charge  when 
fusing. 

Have  the  fire  quite  hot,  place  in  it  the  cru- 
cible, covered,  bank   around   it  with   the   hot 


244  MANUAL    OF  ASSAYING. 

coals,  and  heat  quickly  till  contents  are  in 
quiet  fusion,  which  requires  fifteen  to  twenty 
minutes. 

When  satisfied  that  the  charge  is  well  fused, 
remove  cover,  lift  out  the  glowing  crucible  by 
means  of  the  long -handled  crucible  tongs 
(figs.  37  to  41),  and  tap  it  gently  on  a  brick 
three  or  four  times  (in  order  to  gather  into 
one  button  any  little  pellets  of  molten  lead 
that  may  be  scattered  throughout  the  fused 
mass),  then  cover,  and  let  stand  till  cold. 

When  stone-cold,  break  the  crucible,  detach 
from  all  adhering  slag  the  lead  button  (if 
there  is  any),  hammer  into  shape  as  usual, 
and  weigh  it. 

We  shall  have  one  of  two  alternatives  : 
i  st.    A  lead  button. 
2d.     No  lead  button. 

ist  Case.     A  lead  button  is  obtained. 

This  result  shows  that  the  ore  has  a  reduc- 
ing action  —  the  weight  of  the  button  will 
indicate  its  power. 

There  will  be  then  one  of  three  results  : 


GOLD   AXD    SILVER   ORES.  245 

A.  The  lead  button  has  a  weight  less  than 
one-half  that  of  the  ore. 

B.  The   lead   button   has    a  weight   about 
equal  to  one-half  that  of  the  ore. 

C.  The  lead  button  has  a  weight  greater 
than  one-half  that  of  the  ore. 

I  take  each  supposition  in  turn. 

A.  The  lead  button  has  a  weight  less  than 
one-half  that  of  the  ore. 

Rule.  —  Multiply  the  weight  of  the  lead 
button  by  20  (to  ascertain  what  the  standard 
weights  of  i  A.T.,  30  grammes  or  480  grains 
would  produce),  and  subtract  the  product  from 
the  standard  weight  of  button  desired  (15 
grammes  or  240  grains).  The  result  is  the 
weight  of  lead  which  must  be  reduced  by  some 
reducing  agent.  Divide  this  by  the  reducing 
power  of  the  reducing  agent  to  be  used,  and 
the  quotient  will  be  the  weight  of  the  reduc- 
ing agent  necessary  to  be  added  in  the  regular 
assay. 

Examples.  —  Suppose  the  -^V  A.  T.  or  i^ 
grammes  of  ore  produced  a  lead  button  weigh- 


246  MANUAL    OF  ASSAYING. 

ing  \  gramme,  then  i  A.  T.  or  30  grammes 
would  produce  Jx2o  =  5  grammes,  15  —  5  =  10, 
so  that  the  lead  button  lacked  10  grammes  of 
the  standard  weight.  We  have  therefore  that 
amount  to  be  reduced  by  an  added  reducing 
agent.  Taking  charcoal  as  25  and  dividing 
that  into  the  10  gives  us  f  gramme  as  the 
weight  of  charcoal  to  be  employed. 

In  a  similar  manner  would  we  proceed  when 
gr'ain  weights  are  used.  If  24  grains  of  ore 
reduced  4  grains  of  lead,  then  4x20  =  80;  240— 
80=160;  i6o-f-25  =  6f-  =  grains  of  charcoal  to 
be  used. 

Should  the  particular  sample  of  charcoal 
employed  possess  a  greater  or  lesser  reducing 
power  than  25,  or  should  argol  (reducing 
power  about  7^),  or  flour  (reducing  power 
about  15),  or  any  other  reducing  agent  be 
made  use  of,  then  simply  substitute  in  the 
above  calculations  the  appropriate  figures. 

B.  The  lead  button  has  a  weight  aboiit  eqiial 
to  one-half  that  of  the  ore. 

This  case  is  very  simple.     The  quantity  of 


GOLD  AND   SILVER   ORES.  247 

ore  taken  for  the  regular  assay  will,  of  course, 
as  in  the  preliminary  assay,  reduce  half  its 
own  weight  of  lead  (giving  buttons  of  about 
the  right  size),  hence  there  is  needed  no  ad- 
ditional reducing  action. 

C.  The  lead  button  has  a  weight  greater 
than  one-half  that  of  the  ore. 

Here  we  have  an  instance  of  too  great  a 
reducing  action,  hence  the  excess  of  lead  must 
be  oxidized  away,  or,  to  put  it  more  correctly, 
we  must  supply  enough  oxygen  to  satisfy  that 
proportion  of  the  reducing  elements  of  the 
ore  which  would  reduce  the  excess  of  lead, 
and  then  they  will  leave  the  oxygen  of  the 
litharge  alone.  The  oxygen-supplying  medium 
is  nitre. 

Rule.  —  Multiply  the  weight  of  the  lead 
button  by  20,  and  subtract  from  the  product 
the  standard  weight  of  button  desired.  The 
result  is  the  excess  of  lead  which  is  to  be  re- 
tained in  the  form  of  litharge  by  use  of  nitre. 
Divide  this  by  the  oxidizing  power  of  the 


248  MANUAL    OF  ASSAYING. 

nitre*    used,    and    the    quotient    will    be    the 
weight  of  the  latter  to  be  employed. 

Examples.  —  Suppose  the  -fa  A.  T.  or  the 
i£  grammes  of  ore  produced  a  lead  button 
weighing  3.15  grammes,  then  i  A.  T.  or  30 
grammes  would  produce  3. 15x20=63  grammes, 
63 — 1 5 =48= weight  of  lead  to  be  kept  oxidized 
48-^4=12  =  grammes  of  nitre  to  use. 

If  the  grain  weights  are  used,  and  the  24 
grains  of  ore  have  reduced  say  50  grains  of 
lead,  then  50  x  20  =  1,000  ;  1,000—  240  =  760, 
760-^-4=190=  grains  of  nitre  to  keep  oxidized 
the  760  grains  of  unnecessary  lead. 

The  various  sulphurets  possess  varying  re- 
ducing powers ;  hence,  by  starting  with  a 
knowledge  of  the  reducing  power  of  each 
kind  of  sulphuret,  and  estimating,  by  the  eye, 
the  proportion  or  percentage  of  whatever  kind 
may  be  in  the  ore  in  question,  we  may  ap- 
proximate pretty  closely  to  the  amount  of 
nitre  to  add  in  order  to  oxidize  all  the  sulphur 
but  that  which  we  want  present  to  bring  down 

*  One  part  of  nitre  oxidizes  four  parts  (very  nearly)  of  lead. 


COLD  AND   SILVER    ORES. 


249 


the  proper  weight  of  lead,  and  so  can  avoid 
making  a  preliminary  assay.  The  adjoining 
table  will  be  found  useful  for  reference  : 


Percentage  of 

the  sulphu- 

Parts of  lith- 

ret   which 
with  charg- 

Parts    of 

KIND 

OF 
SULPHURET. 

arge     re- 
quired   to 
completely 
oxidize    i 
part  of  the 
sulphuret. 

Parts  of  me- 
tallic   lead 
reduced    by 
i  part  of  the 
sulphuret. 

es  of  i  A.T., 
30  grms.  or 
480    grains, 
will   reduce 
a  lead   but- 
ton of  about 
15  gram- 

nitre re- 
quired to 
complete- 
ly oxidize 
i  part  of 
the  sul- 
phuret. 

mes   or  240 

grains. 

i.   Zinc  blende  ... 

25 

6,5 

7-7 

2.   Manganblende  . 

30 

6-7 

7-5 

3.    Iron  pyrites    ... 

50 

8.6 

5-8 

2.5 

4.  Arsenopyrite  .  .  . 

40 

7-3 

6-5 

5.   Copper  pyrites  . 

30 

7-2 

7 

6.   Copper  glance  . 

25 

3-8 

13 

7.   Gray  copper  .  .  . 

35 

6 

S 

8.   Gray  antimony  . 

25 

5-7 

9 

9.  Galena  

1.8 

2.8* 

18 

! 

*  All  the  lead  of  the  galena  and  litharge. 

Should  the  assayer  decide  to  roast  the  ore, 
of  course  it  will  not  be  necessary  to  make  a 
preliminary  assay  to  determine  its  reducing 
power,  as  the  roasting  will  eliminate  the  re- 
ducing elements.  But  it  should  be  remem- 


250  MANUAL    OF  ASSAYING. 

bered  that  the  roasting  converts  the  sulphu- 
rets  of  copper,  iron,  manganese,  and  lead,  and 
their  lower  oxides,  into  the  higher  oxides  of 
the  same  metals.  It  will,  therefore,  make 
their  ores  highly  oxidizing,  requiring  a  greater 
amount  of  reducing  agent  .in  the  actual  assays, 
and,  perhaps,  necessitate  preliminary  assays 
to  determine  their  oxidizing  powers,  as  shown 
in  the  succeeding  paragraphs. 

2d  Case.     No  lead  button  is  obtained. 

This  result  shows  conclusively  that  the  ore 
has  no  reducing  action.  It  may  also  have  no 
oxidizing  action  ;  but,  on  the  other  hand,  it 
may.  In  case  it  has  no  oxidizing  action,  then, 
for  the  regular  assay,  take  such  an  amount  of 
whatever  reducing  agent  is  used  as  will  pro- 
duce the  proper  weight  lead  button. 

Thus: 


Grammes    or    Grains  Of  ordinary 

2!  38  Cream  of  tartar 

ij  28  Argol 

i  16  Flour 

•J.  8  Charcoal 


Will   reduce 

a  lead  button 

>  of     about     15 

grammes  or 

240  grains. 


GOLD  AND    SILVER   ORES.  251 

To  determine  the  exact  oxidizing  power  of 
the  ore,  prepare  and  run  the  following 

PRELIMINARY    CHARGE  TO    DETERMINE  OXIDIZING    POWER. 

A.  T.  Weights,  Gramme  Weights,  Grain  Weights. 

Litharge . .    i       A.T.  30    grammes.  480    grains. 

Ore JF     "  4         "  24 

Charcoal..  .050  grms.  .050           "  £       " 
Salt  cover. 

Use  a  "W"  crucible,  treat  in  the  usual 
manner,  and  weigh  resulting  button. 

As  in  the  tests  for  reducing  powers,  there 
will  be  either  : 

i st.    A  lead  button. 
2d.     No  lead  button. 

ist  Case.     A  lead  button  is  obtained. 

The  weight  of  the  lead  button  will,  of 
course,  vary,  giving  rise  to  one  of  three  re- 
sults : 

A.  The  lead  button  has  a  weight  less  than 

o 

one-half  that  of  the  ore. 

B.  The  lead   button    has    a  weight  about 
equal  to  one-half  that  of  the  ore. 


252  MANUAL    OF  A SSA  YING. 

C.  The  lead  button  has  a  weight  greater 
than  one-half  that  of  the  ore. 

To  proceed  in  regular  order. 

A.  The  lead  button  has  a  weight  less  than 
one-half  that  of  £he  ore. 

Rule. —  Multiply  the  weight  of  the  lead  but- 
ton by  20  (to  bring  the  calculations  up  to  the 
standard  weights  of  i  A.  T.,  30  grammes  or 
480  grains),  and  subtract  the  product  from  15 
or  240.  The  difference  is  a  part  of  the  amount 
of  lead  kept  oxidized  by  the  standard  weight 
of  ore  employed,  and  this  action  is  to  be  neu- 
tralized by  an  extra  amount  of  charcoal.  Di- 
vide this  difference  by  the  reducing  power  of 
the  charcoal  used,  and  the  quotient  will  be  the 
weight  of  charcoal  needed. 

Examples.  —  The  figures  given  were  derived 
from  assays  on  an  ore  which  was  composed  of 
about  one-half  silica  and  one-half  red  oxide 
of  iron.  The  charcoal  used  had  a  reducing 
power  of  23.4  —  that  is,  one  part  of  the  char- 
coal reduced  23.4  parts  metallic  lead  from  the 
litharge. 


GOLD   AND    SILVER   ORES.  253 

The  charge  given  was  run  twice,  and  but- 
tons weighing  o. 30  grammes  obtained .  o.  30 x 
20=6.00;  15.00— 6.00=9.00=  grammes  of  lead 
kept  as  oxide  by  the  action  of  the  ore.  9-=- 
23.4=0.384=  grammes  of  charcoal  to  neutral- 
ize this  action.  Hence, 

Grms.  Charcoal.  Grms.  Lead. 

.050X20         =      i. ooo         to  reduce         6.00 

9^-23.4     =     0.384  9.00 

Or  a  total  of  ..      1.384          "        "  15.00 

Had  there  been  no  oxidizing  ore  present, 
the  i  gramme  charcoal  would  have  reduced  a 
button  of  23.4  grammes,  as  stated.  It  actu- 
ally reduced  but  6  grammes  ;  hence,  23.4 — 6= 
=  18.4=  grammes  of  lead  kept  oxidized  by  the 
ore,  but,  as  seen,  we  cared  to  reclaim  only 
9  grammes  6f  this  18.4  grammes  —  the  re- 
mainder can  be  left  oxidized. 

About  the  same  calculations  in  the  grain 
system  would  be  as  follows  :  4.62  grains  = 
weight  of  lead  button  reduced  by  f  grain 
charcoal;  4.62x20  =  92.4;  240—92.4  =  147.6  = 
deficiency  in  grains  of  lead  of  a  240  grain  but- 


254  MANUAL    OF  ASSAYING. 

ton  ;   147.6-^23.4  =  6.3  =  grains  of  charcoal  to 
reduce  that  deficiency.      Hence, 

Grains  Charcoal.  Grains  Lead 
for      0.75X20     =      10.5         to  reduce  92.4 

147.6   -5-23.^=        6.3  147.6 

Or  a  total  of 16.8         ."        "  240.0 

B.  The  lead  button  has  a  weight  about  equal 
to  one-half  that  of  the  ore. 

In  this  case  simply  multiply  the  charcoal 
and  ore  twenty  times  for  the  regular  charge. 
For  example,  an  ore  with  .050  grammes  char- 
coal as  usual  gave  me  a  lead  button  of  0.765 
grammes  ;  hence  for  the  regular  assay  I  took 
i  gramme  charcoal  to  i  A.  T.  or  30  grammes 
ore  to  obtain  a  15  gramme  (15.30)  button. 

In  other  words,  the  ore  oxidizes  such  a  pro- 
portion of  the  charcoal  that  the  remainder  of 
the  latter  is  just  sufficient  to  bring  down  a 
button  of  the  right  size. 

C.  The  lead  button  has  a   weight  greater 
than  one-half  that  of  the  ore. 

Here  we  have  an  example  of  too  slight  an 
oxidizing  action,  which  allows  of  too  great  a 


GOLD   AND    SILVER   ORES.  255 

reducing  action  on  the  part  of  the  charcoal, 
resulting  in  too  large  a  button.  There  is 
then  needed  more  oxidizing  action,  which  is 
effected  by  adding  an  oxidizing  agent,  or, 
which  amounts  to  the  same  thing,  by  lessen- 
ing the  quantity  of  charcoal. 

Rule. —  Multiply  the  weight  of  the  lead  but- 
ton by  20,  and  divide  the  product  by  15  or  240. 
The  quotient  multiplied  by  the  original  amount 
gives  the  right  quantity  of  charcoal  to  reduce 
a  15  gramme  or  240  grain  button. 

Examples. —  Imagine  that  the  charge  on 
a  certain  ore  gave  a  button  of  i.io  grammes. 
This  multiplied  by  20  is  22  grammes,  which 
is  too  large  a  button  ;  hence,  better  diminish 
the  quantity  of  charcoal.  If  i  gramme  char- 
coal with  this  particular  ore  brings  down  a  22 
gramme  button  (instead  of  23.4,  the  ore  ox- 
idizing the  difference  of  1.4  grammes),  then 
15  -h  22  r=o.68  ;  0.68x1  =  0.68  grammes,  the 
amount  which  will  reduce  a  15  gramme  button. 

In  grains,  let  the  lead  button  weigh  17  ;    17 


256  MANUAL    OF  A  SSA  YING. 

grains  x  20  —  340  grains  (too  large  a  button)  ; 
240-^-340=0.7;  0.75x0.7=0.525,  or  say  £  grain. 

2ct  Case.     No  lead  button  is  obtained. 

This  would  show  that  the  ore  is  extremely 
oxidizing,  and  to  learn  its  precise  strength 
necessitates  the  repeating  of  the  preliminary 
with  double,  treble,  etc.,  the  quantity  of  char- 
coal, or  till  a  button  finally  is  obtained.  But, 
in  general,  it  will  be  safe  to  use  twice  the 
weight  of  charcoal  given,  or  for  the  regular 
assay  2  grammes  or  31  grains  where  the  pre- 
liminary produces  no  lead  or  a  very  minute 
button. 

We  have  previously  spoken  of  certain  re- 
ducing elements  in  ores — viz.:  sulphur,  arsenic, 
antimony,  and  zinc.  Aside  from  the  reducing 
action  which  they  exert  upon  the  litharge, 
tending  to  produce  too  much  lead,  their  pres- 
ence in  an  ore  is  apt  to  affect  the  accuracy  of 
the  crucible  assay.  Thus  the  sulphurets  may 
combine  with  oxygen,  forming  oxysulphurets, 
which  possess  the  undesirable  property  of 
taking  silver  with  them  into  the  slag,  or,  if 


GOLD  AND    SILVER    ORES.  257 

they  remain  undetomposed,  they  may  easily 
retain  some  gold.  Arseniates  and  antimoni- 
ates,  whether  existing  naturally  in  the  ore,  or 
whether  formed  by  oxidation  during  the  fusion, 
are  also  liable  to  keep  silver  away  from  the 
lead  button.  Blende  or  other  zinc  ores  car- 
rying silver  may  volatilize  this  metal  or  retain 
it  in  the  slag. 

The  objectionable  elements  mentioned  may 
be  gotten  rid  of  in  two  ways  :  by  oxidation  in 
the  crucible  during  the  fusion,  or  by  a  prelimi- 
nary and  separate  operation  known  as  roasting. 
If  the  sulphur,  etc.,  are  in  small  quantities,  the 
fluxes,  litharge  and  soda,  will  oxidize  them 
into  the  slag.  If  in  large  quantities,  nitre 
must  be  used.  It  is  yet  a  disputed  ques- 
tion among  assayers  whether  to  roast  an  ore 
for  crucible  assay  or  not.  Much  can  be  said 
with  truth  on  each  side.  If  roasting  is  not 
performed  we  save  the  trouble  of  an  extra 
operation,  and  the  danger  of  loss  which  extra 
steps  are  always  likely  to  cause,  including  the 
possibility  of  volatilizing  silver  by  too  great  a 


258  MANUAL    OF  A SSA  YING. 

heat  in  roasting.  On  the  other  hand,  if  roast- 
ing is  not  performed,  and  nitre  is  not  used, 
there  are  the  various  chances  of  loss  of  pre- 
cious metal  already  described.  If  nitre  is 
used,  there  is  danger  of  mechanical  loss  by 
the  foaming  of  the  charge,  which  may  overflow 
the  crucible  or  leave  lead  sticking  to  the  sides, 
high  up;  or  if  too  much  nitre  be  taken,  the  lith- 
arge may  not  be  reduced,  so  care  must  be  ex- 
ercised when  using  it.  My  own  experience 
with  beginners  is  that  they  are  more  success- 
ful when  they  previously  roast  refractory  ores, 
than  when  they  omit  this  step.  It  certainly 
brings  the  ore  into  a  much  more  workable 
condition,  as  the  oxides  of  iron  and  copper 
which  are  usually  left  are  easily  treated.  With 
any  particular  ore  the  safest  way  to  proceed 
is  to  run  duplicate  or  triplicate  assays  on  both 
the  roasted  and  unroasted  sample,  and  then  to 
adopt  or  dispense  with  the  roasting  accord- 
ingly as  the  results  are  richer  with  or  without 
it.  For  the  benefit,  then,  of  learners,  for 
whom  this  book  is  written,  and  not  for  ad- 


GOLD  AND   SILVER   ORES.  259 

vanced  assayers,  I  give  herewith  a  very  care- 
ful description  of  the  manner  of  performing 
this  important  operation. 

Roasting. — Weigh  the  ore  carefully,  sam- 
pling as  usual.  Next  transfer  it  to  a  sheet  of 
black  glazed  paper,  and  mix  with  it  about  its 
own  bulk  of  fine  charcoal.  The  latter  is  usu- 
ally recommended  only  when  arseniates  and 
antimoniates  are  present  or  likely  to  be  formed 
by  a  plain  roasting  ;  but  I  consider  it  advisable 
to  use  it  every  time,  for  one  cannot  always 
tell  when  small  quantities  of  arsenic  and  an- 
timony are  in  the  ore,  besides  which,  the  char- 
coal aids  in  expelling  the  sulphur,  and  in  indi- 
cating the  termination  of  the  roasting.  At 
the  worst,  it  can  do  no  possible  harm.  If  the 
ore  should  contain  much  sulphide  of  lead 
(galena)  or  sulphide  of  antimony  (antimony 
glance),  both  of  which  are  quite  easily  fusible, 
add  to  the  ore  and  charcoal  on  the  paper 
some  fine  sand  or  precipitated  silica,  and  mix 
all  well  together,  for  without  this  addition  the 
minerals  while  roasting  would  soon  fuse,  cake 


26O  MANUAL    OF  ASSAYING. 

together,  and  adhere  to  the  dish  or  pan,  thus 
ruining  the  assay.  The  proportion  of  silica 
to  use  depends  upon  the  percentages  of  the 
minerals  named,  it  increasing  as  they  increase 
—  roughly  speaking,  it  can  be  employed  bulk 
for  bulk. 

In  case  the  ore  is  a  sulphide  or  mixture  of 
sulphides  (of  whatever  metal  or  metals),  with 
very  little  or  no  gangue,  it  is  best  to  add  silica, 
to  the  amount  of  at  least  three-fourths  of  the 
weight  of  ore. 

The  contents  of  the  glazed  paper  are  now 
brushed  into  either  a  frying-pan  (page  123), 
or  a  clay  roasting  dish  (page  105),  accord- 
ingly as  an  open  fire  or  the  muffle  is  to  be 
used.  The  frying-pan  should  be  protected 
by  a  coating  of  dry  chalk  or  ruddle  (or  a 
water  paint  of  either  can  be  used  and  the  pan 
dried),  or  plumbago.  The  roasting  dish  may 
be  similarly  protected,  but  it  is  not  so  neces- 
sary. If  the  standard  weights  of  i  A.  T.,  30 
grammes,  or  480  grains  is  used,  the  ore  mix- 
ture can  be  roasted  in  the  largest  roasting 


GOLD  AND   SILVER   ORES.  261 

dish  which  will  go  in  the  muffle  ;  but  above 
those  weights  use  the  frying-pan,  or  else  roast 
several  charges  in  the  dishes,  and  unite  them 
for  fusion. 

Place  the  roasting  dish,  with  contents,  in 
the  forward  part  of  the  muffle,  before  the  latter 
has  reached  a  dull  red  heat.  The  ore  is  to 
be  continually  stirred  with  a  stout  wire,  hav- 
ing a  loop  at  the  end  at  right  angles  to  the 
wire,  ~  ~~A.  In  a  little  while,  minute 

sparks  will  be  thrown  off,  and  the  ore  will 
begin  to  glow  in  places  like  burning  charcoal. 
Stirring  should  be  continued  till  the  glowing 
ceases  (by  which  time  there  will  be  little 
danger  of  fusion),  and  the  whole  seems  of 
one  color,  and  yielding  to  the  stirrer  like  dry 
sand.  The  dish  can  now  be  moved  back  to 
the  hottest  part  of  the  muffle,  and  left  un- 
stirred for  some  little  time.  When,  on  bring- 
ing out  to  the  open  air  and  stirring,  the  ore 
gives  off  neither  fumes  nor  odor,  the  opera- 
tion is  finished,  the  ore  being  now  "  sweet." 
Let  cool,  and  examine. 


262  MANUAL   OF  ASSAYING. 

The  roasted  ore  should  be  of  a  dull,  dead, 
earthy  color  (usually  some  shade  of  red  or 
black),  having  no  metallic  lustre,  containing 
no  large,  hard  lumps,  and  having  no  portions 
adhering  to  the  dish.  See  that  all  the  char- 
coal is  burnt  out.  Should  the  ore  contain 
many  lumps,  grind  in  a  mortar,  mix  with 
charcoal,  return  to  the  dish,  and  repeat  the 
roasting. 

If  the  assayer  is  too  busy  to  spare  the  time 
needed  for  stirring,  let  him  take  the  dish,  and 
spread  its  contents  out  thinly,  or  ridge  the 
ore  from  the  center  to  the  edges,  so  as  to 
increase  the  surface  exposed,  and  place  it  in 
the  muffle,  and  warm  it  gently  for  a  time  ; 
then  increase  the  heat  for  about  the  same 
length  of  time  ;  finally  heat  quite  hot.  Take 
out  dish,  cool,  grind  finely,  return  to  dish,  and 
roast  again.  Repeat  the  roasting  two,  three, 
or  more  times  if  necessary.  All  this  will 
occupy  time,  but  not  the  direct  attention  of 
the  assayer. 

The  roasting  in  the  pan  is  done  similarly. 


GOLD  AND   SILVER   ORES.  263 

Whether  open-air  pan  roasting,  or  dish  in 
muffle  roasting  is  performed,  guard  against 
too  high  a  heat  at  first,  as  that  may  cause 
fusion,  or  too  sudden  a  delivery  of  the  vola- 
tile metals  mentioned,  which  may  carry  off 
silver,  or  even  too  great  heat  at  any  stage  of 
the  roasting,  tending  to  volatilize  silver  or 
gold  from  some  of  their  combinations. 

The  roasting  with  charcoal  is  supposed  to 
decompose  all  sulphates,  arseniates,  and  anti- 
moniates,  and  to  expel  them  ;  but  where  the 
ore  was  or  contained  copper  pyrites,  a  certain 
quantity  of  sulphate  may  remain  unchanged. 
Hence,  with  ores  of  this  nature,  mix  the 
roasted  ore  with  from  one-fourth  to  one-half 
its  weight  of  fine  and  dry  carbonate  of  ammo- 
nia. Return  to  dish,  cover  with  an  inverted 
roasting  dish,  and  place  in  a  moderately  warm 
part  of  the  muffle  till  no  odor  of  ammonia 
can  be  perceived.  The  sulphate  of  copper  is 
converted  into  sulphate  of  ammonia,  which, 
being  very  volatile,  is  quickly  driven  off. 

If  the  laboratory  is  provided  with  gas,  the 


264  MANUAL    OF  ASSAYING. 

ore  can  be  roasted  in  the  usual  roasting  dish 
over  the  Fletcher  burners  or  the  Fletcher 
roasting-  furnace,  illustrated  on  page  68,  which 
will  work  very  nicely,  as  the  temperature  can 
be  regulated  to  any  degree. 

Methods  of  the  crucible  assay. — There  are 
two  general  methods  or  systems  of  crucible 
assays  in  use  in  this  country.  The  first,  more 
ancient,  better  known,  and  more  commonly 
used  one  employs  an  excess  of  litharge,  and 
we  can  therefore  consistently  call  it  the  lith- 
arge crucible  process.  Mr.  C.  H.  Aaron,  in 
his  very  valuable  little  work  on  assaying, 
designates  it  as  the  first  system,  while  another 
method,  which  he  is  the  first  to  describe,  he 
calls  the  second  system.  In  justice  to  him,  I 
prefer  to  call  it  Aaron  s  crucible  process. 

The  distinction  between  the  two  systems  is 
this :  The  first  mentioned  uses  litharge  for 
two  purposes,  to  furnish  lead  enough  for  a 
lead  button  to  retain  the  gold  and  silver,  and 
to  aid  in  fluxing  the  ore,  hence  an  excess  of 
the  litharge  is  employed.  The  second  uses 


GOLD   AND    SILVER   ORES.  265 


just  enough  litharge  to  provide  lead  for  the 
lead  button. 

In  the  first,  the  excess  of  lead  not  only 
slags  off  the  gangue,  but  it  oxidizes  all  the 
base  metals,  save  lead,  and  takes  them  also 
into  the  slag.  In  the  second,  the  gangue  is 
slagged  by  soda,  borax,  or  silica,  while  the 
base  metals  are  either  volatilized,  united  with 
sulphur  into  a  matte,  or  combined  with  iron. 

Any  ore  may  be  assayed  by  either  of  these 
processes,  but  each  is  better  suited  to  certain 
classes. 

Mr.  Aaron  argues  that  while  an  assay  by 
the  litharge  process  "  is  quickly  made,  and 
generally  gives  accurate  results,"  yet  "  it  has 
the  disadvantage  of  requiring  considerable 
modification  for  the  various  ores,  as  to  the 
fluxes  proper,  and  to  the  reducers  or  oxidizers 
by  which  the  production  of  lead  is  controlled. 
Sometimes  a  preliminary  assay  is  necessary." 

For  his  process  he  claims  the  following 
advantages  :  "  The  right  quantity  of  lead 
may  nearly  always  be  got  at  once,  for,  al- 


266  MANUAL   OF  ASSAYING. 

though  any  lead  which  the  ore  may  contain 
will  inevitably  come  down  together  with  that 
from  the  litharge  used,  yet  this  can  be  allowed 
for  by  reducing  the  quantity  of  litharge,  or 
omitting  it.  As  litharge  yields  ninety-three 
per  cent  of  lead,  it  is  not  difficult  to  make 
the  adjustment  nearly  enough.  Galena  con- 
tains eighty-six  per  cent  of  lead  ;  hence,  if  the 
ore  is  nearly  pure  galena,  but  little  litharge  is 
needed.  The  method  requires  but  slight 
modification  for  different  ores,  and  may  with 
little  disadvantage  be  made  universal.  The 
button  is  never  much  contaminated  by  cop- 
per, as  it  often^  is  in  the  other  system,  unless 
a  very  large  proportion  of  litharge  is  used, 
which  is  disadvantageous  in  some  ways.  The 
crucible  is  but  little  attacked,  and  the  assay  is 
not  liable  to  boil  over.  The  method  is  es- 
pecially useful  for  ores  carrying  much  galena 
or  other  sulphuret,  and  when  copper  in  any 
form  is  present."  An  additional  advantage, 
resulting  from  the  above,  as  remarked  by  Mr. 


GOLD  AND   SILVER    ORES.  267 

Aaron  elsewhere,  is  the  saving  in  litharge 
and  crucibles. 

My  own  experience  with  Mr.  Aaron's  pro- 
cess shows  that  it  takes  considerably  more 
time  than  does  the  litharge  process,  and  that 
beginners  find  it  more  difficult  to  operate, 
and  to  get  satisfactory  results. 

The  student  can  take  his  choice  of  either 
process,  apply  it  to  any  ore,  and  experiment 
till  he  strikes  that  combination  of  correct 
proportion  of  the  ingredients  of  the  charge, 
degree  of  heat,  and  length  of  time  in  furnace, 
which  will  give  him  the  best  results. 

Let  him  remember  that  the  principles  of 
fluxing  are  true  for  either  process. 

Preparation  of  the  charge.  After  having 
obtained  a  knowledge  of  the  ore  by  tests 

o  » 

based  upon  the  study  of  all  the  preceding, 
the  proper  charge  is  made  up.  Further  on  I 
have  given  special  charges  and  directions  for 
certain  ores,  but  here  I  make  it  only  general. 
The  most  convenient  and  commonly  used 
amount  of  ore  is  either  one  of  the  standard 


268  MANUAL   OF  ASSA  YING. 

weights  I  have  so  frequently  spoken  of,  viz.: 
i  A.  T.,  30  grammes,  or  480  grains.  If  a 
very  low  grade  gold  ore  is  under  examination, 
the  above  quantities  can  be  doubled,  trebled, 
or  quadrupled,  or,  if  necessary,  ten  or  even 
twenty  times  the  standard  weight  may  be 
used.  But  such  large  quantities,  with  the 
fluxes  accompanying,  are  rather  difficult  to 
handle,  so  that  it  is  best  to  run  several 
charges  of  the  standard  weight  (or,  perhaps, 
double  it),  and  to  unite  the  resultant  buttons 
by  scorification.  If  it  should  happen  that 
there  is  not  enough  of  the  ore  to  make  a  fair 
charge  (say  not  half  the  standard  weight), 
then  do  not  trouble  about  the  crucible  process 
at  all,  but  treat  the  sample  by  scorification. 

Bi-carbonate  of  soda,  or,  as  it  is  commonly 
called,  soda,  is  used  in  every  crucible  assay. 
Although  not  absolutely  necessary,  still  a 
mixture  of  it  with  carbonate  of  potash  gives 
somewhat  more  fluid  slags.  About  one  part 
of  the  latter  to  four  parts  of  the  former  is  a 
good  proportion.  Considering  the  ore  as  one 


GOLD   AND    SILVER   ORES.  269 

part,  the  amount  of  soda  (or  of  soda  and  car- 
bonate of  potash  together)  varies  from  one- 
half  to  three  parts.  A  safe  quantity  to  use  is 
two  parts.  . 

Litharge  is  also  used  in  all  crucible  assays 
save  those  of  ores  very  rich  in  lead.  The 
proportion  varies  from  one  part  to  eight 
parts — one  to  two  parts  being  the  usual 
range. 

Silica  is  usually  employed  only  for  ores  full 
of  lime,  magnesia,  baryta,  etc. ;  in  short,  for 
those  whose  gangues  are  basic,  or  when  the 
ore  contains  no  gangue;  but  I  make  it  a  uni- 
versal rule  to  use  it  in  all  crucible  assays. 
For  those  ores  which  have  no  gangues  or  are 
basic,  it  is  certainly  needed.  For  those  which 
contain  silica  I  still  add  it,  to  be  certain  to 
convert  the  excess  of  lead  over  and  above 
that  required  for  the  standard  weight  of  lead 
button  into  silicate  of  lead,  a  most  efficient 
flux.  This  for  ores  worked  by  the  litharge 
process.  In  those  treated  by  Aaron's  pro- 
cess, the  added  silica  converts  the  soda  into 


2  7O  MA NUAL   OF  A SSA  YING. 

silicate  of  soda  (or  soluble  glass),  a  good 
flux,  although  not  so  powerful  as  the  lead 
glass.  For  pure  carbonate  of  lime  and  similar 
gangues,  use  the  same  weight  of  silica  as  of 
ore.  For  pure  quartzose  ores,  one-half  the 
weight  of  ore.  For  less  pure  quartz,  three- 
fourths  the  weight  of  ore.  In  brief,  my  final 
advice  is,  not  to  be  afraid  of  using  plenty  of 
silica  in  crucible  charges. 

Borax  is  best  used  in  the  form  of  borax 
glass.  For  quartzose  ores,  none  is  absolutely 
needed,  but  about  10  per  cent  the  weight  of 
ore  does  no  harm,  and  seems  to  help  the 
fusion.  Strongly  basic  ores  need  50  per  cent 
of  borax  glass.  As  they  diminish  in  lime, 
etc.,  clown  to  quartz  ores,  diminish  the  borax 
glass  down  to  10  per  cent. 

Charcoal  and  other  reducing  agents,  and 
the  oxidizing  agent,  nitre,  are  to  be  used 
according  to  their  several  powers  and  as  the 
ores  vary. 

It  should  also  be  remembered  that  where 
gas  furnaces  are  constantly  used,  there  will 


GOLD  AND   SILVER   ORES. 


not  be  required  so  much  reducing  agent  in 
the  crucible  charges  as  in  those  made  up  for 
solid  fuel  furnaces,  the  flame  and  heat  of  the 
gas  furnaces  being  more  reducing. 

A  cover  of  salt  is  to  be  invariably  used. 

Select  the  crucibles,  which  should  be  free 
from  cracks  and  flaws.  A  good  size  for  the 
charges  to  go  with  the  standard  weights  of 
ore  is  4^  inches  wide  by  4^  inches  deep, 
outside  measurement  (size  "S"  of  Battersea 
make).  Clean  the  crucibles  inside  if  they 
need  it,  and  number  or  letter  each  by  means 
of  liquid  ruddle,  in  several  places  and  in  large 
characters,  that  there  may  be  no  difficulty  in 
identifying  them  after  fusion. 

Weigh  out  next  the  soda  for  the  charge, 
and  brush  on  to  a  clean  piece  of  black  glazed 
paper.  Next  weigh  the  litharge  very  care- 
fully, and  brush  on  top  of  the  soda.  The 
silica,  weighed  approximately,  is  followed  by 
the  ore,  charcoal,  or  other  reducing  agent,  or 
nitre,  each  weighed  carefully.  If  sulphur  is 
used,  it  can  come  next.  Finally,  weigh  the 


272  MANUAL   OF  ASSAYING. 

carbonate  of  potash,  rapidly  and  but  approx- 
imately, as  it  quickly  absorbs  moisture  from 
the  atmosphere;  transfer  to  the  paper,  and 
mix  everything  thoroughly. 

Brush  the  charge  into  the  proper  crucible, 
which  it  will  probably  fill  two-thirds,  tap  gen- 
tly till  the  contents  are  level,  drop  the  weighed 
borax  glass  on  top,  and  cover  with  about  one- 
half  inch  common  salt.  If  nails  are  used,  in- 
sert them  in  the  charge  before  the  salt  is 
added. 

Another  method  of  charging  or  "dressing" 
the  crucibles  is  to  pour  the  soda  into  the  cru- 
cible, then  the  ore,  following  with  the  other 
fluxes,  and  mixing  all  together  in  the  crucible 
with  any  convenient  utensil,  as  a  spatula, 
spoon,  or  glass  rod. 

The  marking  of  the  crucibles  may  be  dis- 
pensed with  if  the  fusions  are  made  in  regular 
order;  but  in  this  case,  great  care  must  be 
exercised,  for  doubt  once  entertained  as  to 
the  identity  of  any  crucible  may  dispel  faith 
in  those  following  or  preceding  it. 


GOLD  AND   SILVER   ORES.  273 

Running  the  Crucibles  in  the  Fire. 

Have  the  fire  quite  hot,  and  place  on  the 
coals  the  crucible,  holding  it  with  the  tongs 
with  one  hand,  and  banking  it  around  with 
the  fuel  till  it  sets  firmly  and  uprightly  in 
place.  Place  the  cover  on,  and  surround  with 
coke,  charcoal,  or  coal,  as  the  case  may  be. 
Coke  works  the  best  when  of  about  the  size 
of  an  egg,  charcoal  may  be  in  somewhat 
smaller  pieces.  The  finer  particles  of  either 
are  often  useful  when  the  fire  gets  too  hot, 
by  choking  the  draft.  Arrange  the  draft 
and  damper  so  as  to  permit  of  a  gradually 
increasing  heat. 

Occasionally  examine  the  crucible  to  see  if 
all  is  working  smoothly.  In  from  twenty-five 
to  forty-five  minutes  the  contents  of  the  cru- 
cible should  be  in  quiet  fusion.  The  length 
of  time  that  a  charge  requires  to  be  thor- 
oughly melted  in  depends  so  much  upon  the 
ever  varying  conditions  of  temperature  of  the 
furnace,  character  of  ore,  size  and  nature  of 


274  MANUAL    OF  ASSAYING. 

charge,  etc.,  that  no  exact  rule  can  be  given  — 
only  see  that  the  charge  is  fused. 

When  satisfied  of  this,  remove  cover,  lift 
out  the  glowing  crucible  by  means  of  the  long- 
handled  crucible  tongs,  tap  gently,  cover,  and 
let  cool,  or  pour  into  the  scorification  mould, 
which  will  hold  the  button  and  some  of  the 
slag  ;  the  excess  of  the  latter  can  run  to 
waste. 

If  nails  have  been  used,  before  tapping  or 
pouring  rinse  each  nail  in  the  slag,  tap  and 
remove.  No  lead  should  adhere  to  them. 

Crucibles  that  have  had  their  contents 
poured  out  can  be  employed  a  second  time,  or 
even  more  often.  In  case  of  ores  that  have 
shown  little  or  no  gold  or  silver  this  may  do, 
but  with  ores  of  any  richness  it  is  a  danger- 
ous experiment.  Accuracy  should  never  be 
sacrificed  to  a  spirit  of  false  economy. 

Never  try  to  cool  a  crucible  by  dipping  it 
into,  or  holding  it  under,  cold  water,  as  the  but 
partially  cooled  lead  is  liable  to  separate  into 


GOLD   AND    SILVER   ORES. 


globules  of  various  sizes,  incurring  danger  of 
loss. 

When  stone-cold,  break  the  crucible  by 
striking  it  a  few  sharp  blows  down  one  side 
with  a  hammer.  If  skilfully  done,  the  cruci- 
ble will  separate  in  halves  the  entire  length, 
exposing  the  lead  button.  Such  a  section 
would  appear  about  as  here 
shown,  showing  at  the  bottom 
the  lead  button  containing  the 
gold  and  silver,  above  it  the 
slag,  and  topping  all  a  layer 
of  fused  salt.  (The  thin  body 
just  above  the  button  shows  FIG.  92. 

how  a  "matte"  would  appear  were  any  formed 
by  the  fusion  of  a  sulphuret.) 

From  the  broken  crucible  or  the  poured 
charge  in  the  mould  save  a  piece  of  the  slag 
for  future  examination  and  comparison.  It 
should  be  uniform  in  color  and  composition 
-the  former  will  vary  with  the  character  of 
the  ore  and  proportions  of  the  ingredients  of 
the  charge.  If  the  latter  has  been  poured, 


276  MANUAL    OF  ASSAYING. 

the  crucible  should  be  but  little  corroded,  and 
smoothly  lined  with  a  thin  glaze  of  the  slag, 
and  retain  no  lumps  of  semi-fused  nature  or 
pellicles  of  lead. 

Free  the  button  from  the  slag,  which  it 
should  easily  and  cleanly  leave,  hammer  into 
shape,  as  usual,  and  mark.  It  may  be  well  to 
weigh  it,  so  that  the  assayer  may  know 
whether  he  has  used  the  proper  quantity  of 
reducing  or  oxidizing  agent,  etc.,  or  to  modify 
the  treatment  on  the  same  or  similar  ores  in 
the  future. 

If  the  button  is  too  large,  it  may  be  re- 
duced by  scorification  ;  but  this  introduces  an 
additional  step,  and  may  not  give  quite  so 
accurate  a  result. 

Finally,  cupel  the  button,  weigh,  part,  in- 
quart,  etc.,  as  previously  directed. 

With  all  ores  poor  in  silver,  deduct  the 
silver  known  to  be  in  the  litharge,  according 
to  the  amount  of  the  latter  employed. 

General  Charges. — From  what  has  been  pre- 
viously written  of  the  varying  characters  of 


GOLD  AND   SILVER   ORES.  2JJ 

ores  the  student  can  see  how  difficult,  if  not 
impossible,  it  is  to  give  a  charge  of  fluxes, 
etc.,  which  shall  satisfy  every  ore.  Still,  there 
are  a  few  general  formulae  useful  to  have  and 

o 

quite  easy  to  remember,  which  can  be  more  or 
less  modified  to  suit  any  particular  ore. 

MITCHELL'S  CHARGE  FOR  ALL  GOLD  AND  SILVER  ORES. 

Ore i  part. 

Soda i      " 

Litharge 5  parts. 

Borax  glass i   part. 

Nitre  or  charcoal  and  always  a  cover  of  salt. 

The  above  in  each  of  the  three  systems  of 
weights  : 

A,  T.  Weights,      Gramme  IV eights.          Grain  Weiglits. 

Ore i  A.T.     30  grammes      480  grains=  i  oz. 

Soda i     "        30         "  480       "      =i    " 

Litharge  ....5     "      150         "  2,400       "      =5  -" 

Borax  glass ..  i     "        30         "  480       "      =  i    " 

Salt  cover. 

A  similar  but  more  commonly  used  propor- 
tion is  : 


278  MANUAL    OF  ASSAYING. 

Ore , i     part. 

Soda i 

Litharge if      " 

Borax  or  silica,  nitre  or  charcoal,  and  salt  cover. 

Or,  to  put  it  more  conveniently  : 

A.  T.  Weights.     Gramme  Weights.         Grain  Weights. 
Ore i       A.T.     30  grammes     48ograins=i     oz. 

Soda i         "        30         "  480       " 

Litharge  . .  if*     "        50         "  800       " 

Salt  cover. 

Mr.  George  L.  Stone  has  published  the  fol- 
lowing as  a  universal  flux  for  basic  silver  ores 
(i.e.,  those  in  which  the  gangue  is  lime,  ba- 
ryta, etc.  —  for  instance,  the  three  spars,  calc- 
spar,  heavy- spar,  and  fluor-spar)  : 

Bi-carbonate  of  soda 9  parts. 

Borax  glass 3       " 

Argol i  part. 

"  Mix  thoroughly,  and  keep  on  hand  ready 
for  use.  For  one-third  assay  ton  of  ore  fill 

*i|  A.T.  or  i.66|  A.T.  cannot  be  exactly  weighed  with  the 
A.T.  weights,  but  the  sum  of  the  following  weights  will  approxi- 
mate it  sufficiently  :  I  A.T.  +0.50  +  0.10  +  0.05  =  1.65. 


GOLD  AND   SILVER   ORES.  279 

the  crucible  about  two-thirds  full  of  the  flux, 
adding  two  or  three  iron  nails  if  the  ore  con- 
tains much  sulphur." 

CHAPMAN'S  CRUCIBLE  FLUX. 

"A  useful  flux,  employed  largely  by  the 
writer  during  the  past  ten  or  twelve  years, 
and  which  has  been  found,  both  in  his  own 
practice,  and  in  that  of  others,  to  yield  good 
results  in  all  general  cases,  has  the  composi- 
tion given  below  : 

3  Ibs.  carb.  soda, 
2    "    dried  borax, 
\  Ib.  cream  of  tartar, 
2  oz.  white  sugar. 

"  The  re-agents  in  these  proportions  must 
be  intimately  intermixed.  The  above  quanti- 
ties will  dress  from  18  to  20  crucibles,  when 
about  25  grammes  of  ore  are  taken  for  assay." 
(Chapman's  Assay  Notes,  1881,  p.  31.) 


28O  MANUAL    OF  ASSAYING. 

AARON'S  GENERAL  FORMULA. 

(For  ores  to  be  worked  by  his  second  system.     See  page  264.) 

Ore i     part. 

Soda 3     parts. 

Litharge , i     part. 

Borax £  part. 

Sulphur TV    " 

Flour TV    " 

Iron 3     nails. 

Glass. 

Salt  to  cover. 

"  Melt,  and  leave  in  strong  fire  about  twenty 
minutes    after    fusion."      (Aaron's    Assaying, 

1884,  p.  530 

The  above  amplified  as  usual  is  as  follows  : 

A.  T.  Weights.  Gramme  Weights.  Grain  Weights. 

Ore i   A.T.  30  grammes  480  grains^  i  oz. 

Soda 3      "  90         "  1,440      " 

Litharge  . .  i      "  30         "  480      " 

Borax J    "  15         "  240      "     =    \  " 

Sulphur...  TV  "  3  48      "     =  TV" 

Flour TV  "  3         "  48      "     =  TV 

Iron 3  nails. 

Glass. 
Salt  cover. 


GOLD   AND    SILVER   ORES.  281 

The  same  excellent  authority,  Mr.  Aaron, 
gives  the  following  charge  for  "  ordinary  ores 
containing  little  or  no  sulphuret,  some  quartz, 
clay,  lime,  iron,  oxide,  etc.  "  : 

Ore i  part. 

Soda i      " 

Litharge 2  parts. 

Dried  borax i  part. 

Flour yig-     " 

Salt  cover. 

"  Fuse  quickly  ;  keep  in  furnace  five  to  ten 
minutes  after  subsidence."  (Aaron,  page  49.) 

Putting  the  above  in  the  three  systems  of 
weights,  and  reducing  the  flour  one-half,  since 
the  quantity  given  is  based  on  a  standard  of 
\  A.  T.  ore,  we  have  the  following  : 

A.  T.  Weights.  Gramme  Weights.        Grain  Weights. 

Ore i  A.  T.  30  grammes  480  grains^  i  oz. 

Soda i  "  30          "  480       "      =  i   " 

Litharge  ...  2  "  60          "  960       "      =2  " 

Dried  borax,  i  "  30          "  480       "      =i   " 

Flour i  grm.        i  grm.              16       " 

Salt  cover. 

The   following  and   concluding   charge    of 


282  MA N UAL  OF  A  SSA  YING. 

this  section  is  one  I  have  used  many  times 
for  ores  similar  to  those  above  spoken  of; 
that  is,  not  containing  much  sulphuret,  or 
oxidized  metal ;  "  dry  ores,"  in  short,  or,  as 
Mr.  Aaron  calls  them,  "  ordinary  ores."  The 
nature  of  the  gangue  is  unimportant,  as  I 
have  gotten  as  perfect  and  as  vitreous  slags 
from  pure  limestones  as  from  pure  quartzose 
rock,  by  using  it. 

A.  T.  Weights.  Gramme  Weights.        Grain  Weights. 

Ore i    A.  T.  30  grammes  480  grains=  i    oz. 

Bi-carb.  soda  i|     "  45  "  720       "      =ij  " 

Carb.  potash  \       "  15          "  240       "      =  i  " 

Litharge  . .  .  i|     «  45          "  720       "      =i|  " 

Silica i       "  30          "  48o       "      =i    " 

Borax  glass.     \     "  15          "  240       "      =i" 

Charcoal  . . .  T6o  grms.  ^          "  9i     " 

Salt  cover. 

The  charcoal  is  used  on  the  basis  of  a 
reducing  power  of  about  25.  Time  in  fire, 
about  one-half  hour. 

Special  charges  and  directions. — I  shall  here 
give  charges  for  certain  well  known  ores,  as 
examples  of  the  varying  modes  of  treatment. 


GOLD   AND   SILVER   ORES.  283 

These  are  iron  pyrites  and  its  oxide,  the  sul- 
phurets  of  copper  and  their  oxides,  and 
galena.  All  other  ores  and  combinations  can 
be  worked  by  some  one  of  the  general  or 
special  methods,  or  some  slight  modification 
of  one  of  them. 

I. IRON    PYRITES. 

Pyrite,  the  true  iron  pyrites,  is  one  of  the 
most  widely  distributed  of  minerals,  is  found 
in  the  rocks  of  every  age,  and  is  a  common 
and  abundant  source  of  gold.  There  are 
many  varieties  of  it,  and  of  another  and  simi- 
lar mineral,  pyrrhotite,  which  have  received 
many  names,  as  pyrites,  iron  pyrites,  pyrite, 
marcasite,  mundic,  bi-sulphuret  or  bi-sulphide 
of  iron,  sulphuret  or  sulphide  of  iron,  and 
pyrrhotite,  magnetic  pyrites,  magnetic  iron 
pyrites,  magnetic  sulphuret  of  iron,  magneto- 
pyrites,  etc.  But  since  the  assay  treatment 
makes  no  mineralogical  distinctions,  I  shall 
include  under  the  one  simple  and  well  known 
heading  of  "  iron  pyrites "  any  combination 


284  MANUAL   OF  ASSAYING. 

of  iron  and  sulphur,  with  or  without  a  gangue, 
and  direct  accordingly. 

Iron  pyrites  has  frequently  united  or  asso- 
ciated with  it  varying  amounts  of  other  met- 
als, as  nickel,  cobalt,  copper,  zinc,  manganese, 
arsenic,  antimony,  etc.  If  in  small  quanti- 
ty, none  of  these  need  influence  the  charge 
or  manner  of  treatment.  If  in  large  quantity, 
making  either  a  compound  mineral,  or  a  com- 
bination of  various  minerals,  they  may  necessi- 
tate some  variation  in  the  mode  of  treatment. 

Since,  as  stated,  iron  pyrites  is  found  in 
rocks  of  every  geological  epoch,  we  may  ex- 
pect to  have  every  kind  of  gangue  ;  but,  by 
remembering  the  rules  already  given,  that 
acid  and  basic  gangues  are  to  have  basic  and 
acid  fluxes,  no  trouble  need  be  feared.  Sil- 
ver, if  present,  will  come  down  with  the  gold. 

METHOD    A. 

Desulphurization  by  a  preliminary  roasting. 
For  the    ore  without  any  gangue,   or   for 


GOLD  AND    SILVER   ORES.  285 

"  concentrates,"  mix  i  part  (i  A.  T.,  30 
grammes,  480  grains)  with  i  part  of  silica. 

Mix  the  above,  or  the  ore  alone,  if  it  has  a 
gangue,  with  its  bulk  of  fine  charcoal,  and 
roast  according  to  pages  259-264. 

After  roasting,  add  the  other  constituents, 
so  that  the  total  charge  will  be  as  follows  : 

CHARGE. 

A.  T.  Weights.    Gramme  Weights.  Grain  Weights. 

Ore  (roasted)  .  i  A.T.     30  grammes  48ograins=i  oz. 

Bi-carb.  soda  .ij   "        45         "  720       "     =ij" 

Carb.  potash  .  J    "        15         "  240       "     =  i  " 

Litharge i£   "        45         "  720       "     =  i£" 

Silica i      "        30         "  480       "     =i    " 

Borax  glass  . .  \   "          6         "  96       "     =  %  " 

*Charcoal . . . .   J  grm.       f       "  n-J-     " 
Salt  cover. 

Use  an  "S"  Battersea  crucible  (4!  inches 
deep,  4-J-  inches  across,  outside  measurement). 
If  it  is  feared  that  a  little  sulphuret  may  re- 
main unoxidized  during  the  roasting,  one  nail 
may  be  pushed  into  the  charge,  and  is  to  be 
removed  immediately  after  fusion. 

*  Assumed  to  have  a  reducing  power  of  25. 


286  MANUAL    OF  ASSAYING. 

Time  in  fire  about  thirty  minutes,  or,  at  all 
events,  let  remain  heating  for  ten  minutes 
after  the  charge  has  settled  into  quiet  fusion. 

It  is  well  to  bear  in  mind  that  iron  pyrites 
(pyrite)  loses  exactly  one-third  of  its  weight 
by  being  roasted  into  the  red  oxide,  so  that 
one  part  of  the  sulphuret  becomes  but  two- 
thirds  of  a  part  of  oxide.  (The  varieties  of 
pyrrhotite  lose  from  one-seventh  to  one-eighth 
in  weight.)  Further,  that  one  part  of  the 
red  oxide  keeps  oxidized  about  \\  parts  of 
litharge,  or,  more  exactly  speaking,  it  oxidizes 
the  charcoal  which  would  reduce  \\  parts 
litharge. 

The  charge  given,  as  stated,  is  for  an  ore 
almost,  if  not  entirely,  iron  pyrites.  From 
such  a  large  percentage  it  may  run  down  to  a 
very  small  amount  of  the  mineral,  the  gangue, 
of  a  necessity,  increasing  accordingly.  If  the 
gangue  is  silicious,  diminish  the  added  silica 
in  the  charge  as  the  proportion  of  gangue 
increases,  but  do  not  altogether  omit  it  for 
even  the  most  silicious  ore  —  retain  from  \  to 


GOLD  AND   SILVER   ORES.  287 


^  a  part.  If  the  ore  is  limey  or  otherwise 
basic,  retain  the  full  part  of  silica,  and  increase 
the  borax  glass  to  \  a  part. 

The  charcoal  (or  any  other  reducing  agent) 
must,  of  course,  be  decreased  as  the  iron  py- 
rites decreases,  for  the  less  there  is  of  the 
latter  the  less  oxidizing  power  there  is  in  the 
roasted  ore.  The  actual  quantity  of  charcoal 
to  use  on  any  particular  ore  is  determined  by 
either  guessing  the  percentage  of  sulphuret 
in  the  unroasted  ore,  or  by  making  a  prelimi- 
nary assay  to  determine  the  oxidizing  power 
of  the  roasted  ore.  Instead  of  doing  the  lat- 
ter additional  work,  the  assayer  can  come 
closely  enough  to  the  size  of  the  button  he 
wants  (15  grammes  or  240  grains)  by  adding 
charcoal  as  the  redness  of  the  roasted  sample 
increases,  and  vice  versa,  as  follows  (the  char- 
coal considered  to  be  of  a  reducing  power 
of  25): 


288  MANUAL    OF  ASS  A  YING. 

Grammes  of 
Color  of  Roasted  Ore.  Charcoal  to  Use. 

Very  deep  red o .  850 

Deep  red o .  800 

Medium  deep  red o .  750 

Red  o .  700 

Medium  light  red  ....    0-675 

Light  red  . . . 0.650 

Very  light  red 0.625 

Very  light  rose  or  pink o .  600 

The  slags  from  crucible  runnings  of  the  ore 
we  are  discussing,  if  the  fusions  have  been 
properly  conducted,  will  always  be  homogene- 
ous and  glassy  in  texture,  and  will  be  translu- 
cent or  transparent  when  not  much  iron  oxide 
is  present,  opaque  when  the  oxide  prepon- 
derates ;  in  color,  ranging  from  very  light 
green  to  a  black,  with  a  greenish  or  grayish 
tint  accordingly  as  the  iron  oxide  increases. 

METHOD    B. 

Desulphurization  during  the  fusion. 
With  ores   treated  by  this   method  we  do 
not  get  rid  of  the  sulphur  of  the  iron  pyrites 
by  a  preliminary  operation,  but  do  the  desul- 


GOLD  AND   SILVER   ORES.  289 

phurizing  during  the  fusion  by  the  oxidation 
of  all  the  sulphur  (save  a  sufficient  quantity 
to  bring  down  a  15  gramme  or  240  grain  but- 
ton) by  means  of  nitre. 

CHARGE. 
For  pure  pyrites  (i.e.,  free  from  gangue)  and  "concentrates."' 

A.  7\  Weights.    Gramme  Weights.         Grain  Weights. 

Ore i    A.T.  30  grammes     480  grains=i  oz. 

Bi-carbsoda  .\\  "  45  "  720  "  =ij" 

Garb,  potash.   £  "  15  "  240  "  =  J" 

Litharge \\  "  45  "  720  "  =i|" 

Silica i  "  30  "  480  "  =  i    " 

Borax  glass..   \  "          6  "  96  "  =  |" 

Nitre 2  "  56^  "  870 

Salt  cover. 

Use  Battersea  "J"  crucible  (6f  inches  deep, 
4f  inches  across,  outside  measurement). 

Time,  about  half  an  hour. 

The  oxidizing  power  of  nitre  varying,  the 
amount  used  may  have  to  be  altered  some- 
what according  to  its  strength,  as  determined 
on  page  162.  The  quantity  taken  was  deduced 
from  the  following  calculation  — » for  example, 
the  weight  in  grammes:  i  gramme  iron  pyrites 
reduces  8.6  grammes  lead  (according  to  the 


2QO  MANUAL   OF  ASSAYING. 

table  on  page  249);  hence,  1.74  grammes  py- 
rites will  reduce  about  15  grammes  lead;  30 — 
1.74  =  28.26=1  grammes  of  iron  pyrites  to  be 
oxidized,  i  gramme  iron  pyrites  requires  for 
oxidation' from  2  to  2\  grammes  nitre;  hence, 
28.26x2  =  56.5=  grammes  nitre  to  use. 

Run  in  good  fire,  twenty  minutes  to  fusion, 
ten  afterward.  Slag  brown-black,  vitreous, 
opaque.  If  the  button  is  at  all  brittle  from 
presence  of  sulphur,  add  lead  and  scorify. 

For  other  ores,  as  the  iron  pyrites  diminishes 
(and  the  gangue  increases),  lessen  the  silica 
and  nitre.  The  quantity  of  the  latter  to  use 
is  determined  by  experience  and  experiment, 
or  by  ascertaining  the  reducing  power  of  the 
ore,  for  which  latter  see  page  242. 

METHOD  c. 
Desulphurization  during  the  fusion. 

This  method  of  treating  the  ore  is  to  use 
an  excess  of  nitre,  i.e.,  more  than  enough  to 
oxidize  all  the  sulphur,  bringing  everything 
into  quiet  fusion,  and  then  throwing  down 


GOLD   AND    SILVER   ORES.  29! 


the  proper  weight  of  lead  by  adding  a  known 
amount  of  some  reducing  agent,  as  charcoal, 
or  a  mixture  of  charcoal  and  litharge,  or 
galena  and  litharge.  The  reduced  lead  in  its 
passage  down  through  the  molten  charge  ab- 
sorbs the  gold  and  silver. 

CHARGE. 

For  iron  pyrites  with  no  gangue,  or  concentrates. 
A.  7\   Weights.      Gramme  Weights.       Grain  Weights. 

Ore i   A.T.     30  grammes    480  grains=i  oz. 

Bi-carb.  soda.i-|  "         45         "  720       "     =i£" 

Carb.  potash.  -£  "         15         "  240       "     =  £  " 

Litharge 6     "       175         "          2,880        "     =6    " 

Silica 2     "         60         "  960        "     =2    " 

Borax  glass.. i     "         30         "  480       "     =i     " 

Nitre 2-£  "         75         "          1,200        "     —  2%  " 

Salt  cover. 

Use  a  "J"  crucible. 

Begin  with  a  very  gentle  heat,  and  grad- 
ually bring  up  to  a  full  red  heat  (thirty-five 
minutes).  When  in  full  fusion  add  the  fol- 
lowing weight  of  charcoal  wrapped  in  tissue 
paper  (considering  the  weight,  of  the  paper 
as  charcoal)  : 

i  gramme,  or  15^  grains. 


292  MANUAL    OF  ASSAYING. 


When  again  in  quiet  fusion  (five  minutes), 
remove  and  tap,  or  pour.  Slags  brownish- 
black,  vitreous,  opaque. 

For  less  pyritic  ores  use  less  nitre. 

METHOD    D. 

Desulphurization  with  iron. 

CHARGE. 

Make  up  the  ore  with  fluxes  as  follows: 

A.  T.   Weights.  Gramme  Weights.  Grain  Weights. 

Ore i  A.T.  30  grammes  480  grains  —  i  oz. 

Bi-carb.  soda.i^   "  45         "  720        "     =i-J- " 

Carb.  potash.   4  "  15         "  240        "     —  -j-  " 

Litharge 1£  "  45  720        "     =  1^  " 

Silica i     "  ,30  480        "     =i     " 

Borax  glass..  -J-  "  6  96 
Iron  nails,  6. 
Salt  cover. 

Use  "  S  "  crucible.     Time,  one-half  hour. 

Tie  the  nails  with  wire  together,  and  stick 
the  bunch  into  the  charge,  points  down. 
After  fusion,  should  any  "  matte  "  be  formed, 
it  must  be  scorified,  with  the  lead  button,  to 
a  pure  and  malleable  condition. 
•  Slags  brown-black,  vitreous,  opaque. 


GOLD  AND    SILVER   ORES.  293 

METHOD    E. 

Converting  the  iron  pyrites  into  matte. 
Aaron  s  process  (modified). 

CHARGE. 

For  concentrated  pyrites. 

A.  T.    Weights.      Gramme  Weights.        Grain   Weights. 
Ore i  A.T.     30  grammes     480  grains  =   loz. 

Bi-carb.  soda. 3  "  90                     1,44°  "  =  3     " 

Litharge \  "  15  "             240  "  =r  1  " 

Silica i  "  30  "             480  "  =i     " 

Borax  glass.,   •£•  "  15  "             240  "  —   |  "' 

Nitre f  "  12  "                18*  " 

Iron  nails,  6. 
Salt  cover. 

Use  "  S"  crucible.     Time  forty  minutes. 

The  nitre  is  to  oxidize  the  excess  of  sul- 
phur ;  i.e.,  that  over  and  above  the  amount 
necessary  to  reduce  all  of  the  litharge,  and 
yet  not  enough  of  this  re-agent  is  used  to 
prevent  the  formation  of  a  matte. 

Slag  coal-black,  vitreous,  opaque. 

Mr.  A.  H.  Low,  of  Argo,  Colo.,  has  given 
me  a  good  hint  in  the  crucible  running  of  sul- 
phuret  ores,  which  I  herewith  note.  Make 


294  MANUAL    OF  ASSAYING. 

the  fusion  in  the  usual  manner,  and  when  it  is 
supposed  to  be  completed,  take  out,  and  pour 
off  as  much  of  the  slag  as  possible  without 
losing  any  of  the  lead.  The  button  can  now 
be  easily  seen,  and  if  all  the  sulphur  has  not 
been  driven  off,  replace  the  crucible  in  the 
fire  at  an  angle,  and  scorify,  as  it  were,  till 
the  sulphur  has  gone  ;  take  out,  pour,  and  the 
result  will  be  a  clean  button. 

For  ores  which  are  much  richer  in  gold 
than  silver,  and  in  which  it  is  not  desired  to 
determine  the  latter,  the  operation  of  inquar- 
tation  of  the  resultant  bead  can  be  dispensed 
with  by  putting  in  the  charge  before  running 
a  piece  of  pure  silver  of  the  proper  weight ;  it 
will  help  to  collect  the  gold,  moreover. 

Comments  on  the  Jive  preceding  processes.— 
With  these,  as  with  others,  each  assayer  will 
find  some  certain  one  will,  with  him,  work 
better,  and  give  higher  results  than  the  oth- 
ers. He  can  then  practice  until  he  ascertains 
which  one  suits  him  the  best,  and  always 
employ  that. 


GOLD  AND   SILVER    ORES.  295 

My  own  experiments,  and  those  of  my  stu- 
dents, tend  to  prove  that  each  of  the  first 
three  methods  is  pretty  sure  to  bring  down 
all  the  gold  ;  that  the  fifth  method  must  be 
worked  very  carefully  to  obtain  correct  results, 
and  that  the  fourth  is  the  most  unsatisfactory 
of  all.  Further,  that  the  first  method  gives 
higher  silver  than  any  of  the  others,  which 
supports  the  theory  that,  with  sulphur  in  an 
ore  during  its  fusion,  oxy-sulphureta  are 
formed,  which  drag  silver  with  them  into  the 
slag. 

Many  ignorant  assayers  insist  that  from 
unroasted  sulphuret  of  iron  ores,  no  gold  will 
be  obtained  by  crucible  fusion.  This  extra- 
ordinary idea,  which,  however,  seems  to 
spread,  is  entirely  unfounded,  or,  at  best,  is 
based  upon  botchy  experiments.  The  stu- 
dent may  rest  assured  that  he  can,  with  care- 
ful working,  extract  all  the  gold  from  an 
unroasted  ore  by  any  one  of  the  nitre  meth- 
ods. 


296  MANUAL    OF  ASSAYING. 

II.  —  OXIDE    OF    IRON. 

One  of  the  results  of  the  decomposition  of 
iron  pyrites  is  oxide  of  iron,  existing  either  as 
limonite,  which  is  the  oxide  with  water,  or  as 
hematite,  the  oxide  without  water.  It  is  even 
more  widely  distributed  than  iron  pyrites,  and 
since  the  latter  is  one  of  the  most  common 
sources  of  gold,  so  likewise  is  oxide  of  iron, 
with  the  advantage  that  that  precious  metal 
is  retained  therein  in  a  free-milling  condition. 
It  is  so  universal  that  any  brownish,  yellow- 
ish, or  reddish  coating  on  an  ore  is  almost 
certain  to  be  partially,  if  not  entirely,  oxide 
of  iron. 

The  ore  can  be  treated  in  two  ways,  by  the 
charge  given  for  the  iron  pyrites  after  roast- 
ing (on  page  285),  remembering  that  there 
is  a  full  part  of  this  ore,  against  three-fourths 
of  a  part  of  the  roasted  sulphuret,  or  by 
Aaron's  process. 


GOLD  AND   SILVER   ORES.  297 

CHARGE. — LITHARGE    PROCESS. 

A.  T.  Weights.  Gramme  Weights.        Grain  Weights. 

Ore i    A.  T.  30  grammes  48ograins=i    oz. 

Bi-carb.  soda  i J     "  45                      720       "      =i-J-" 

Garb,  potash    |     "  15           "          240       "      —  -J-  " 

Litharge  ...  \\     "  45                       720       "      =  i£" 

Silica i       "  30           "           480       "      =i     " 

Borax  glass.     \     "  6           "             96       "      —  \    u 

Charcoal  . .  .  i  grm.  i           "             15^     " 
Salt  cover. 

The  above  charge  is,  for  the  oxide  ore, 
quite  free  from  gangue.  As  has  before  been 
stated,  diminish  the  silica  and  charcoal  as  the 
gangue  increases. 

It  may  be  as  well  to  add  a  cautionary  note, 
to  the  effect  that  limonite,  the  hydrous  oxide 
(yellow  or  brown  in  color),  contains  about 
14^  per  cent,  of  water  of  combination,  while 
hematite,  the  red  oxide,  contains  none  what- 
ever; hence  use  more  charcoal,  or  other  reduc- 
ing agent,  for  the  latter  than  for  the  former. 


298  MANUAL    OF  ASSA  YING. 

CHARGE. —  AARON'S  PROCESS  (MODIFIED). 

A.  T.  Weights.  Gramme  Weights.        Grain  Weights. 

Ore i    A.  T.  30  grammes  48ograins=i   oz. 

Bi-carb.  soda  3       "  90          "  1,440    " 

Litharge  . . .     £     "  15  "  240       " 

Silica i        "  30          "          480       "      =i    " 

Borax  glass.     £     "  15  "•         240       "      =  % " 

Sulphur -J     "  15  "          240       "      =  i" 

Flour ^    «  12          "  i8J       « 

Iron  nails,  6 
Salt  cover. 

Many  times  the  assayer  will  meet  ores 
which  are  mixtures  of  iron  pyrites,  and  its 
decomposed  substitute,  iron  oxide.  Such 
must  be  treated  by  the  methods  given  for  the 
former  mineral.  If  the  pyrites  is  in  very 
small  quantity,  Process  A,  without  a  prelimi- 
nary roasting,  may  be  used  (in  this  case  em- 
ploy but  from  one-third  to  one-half  the 
amount  of  charcoal),  as  the  fluxes  will  do  all 
the  necessary  desulphurizing. 

III. SULPHURETS    OF    COPPER. 

Including  sulphuret  of  copper  (chalcocite, 
copper  glance,  vitreous  copper,  copper  sul- 


GOLD  AND   SILVER   ORES.  299 

phide),  which  when  pure  contains  79.8  per 
cent  of  copper  and  20.2  per  cent  sulphur,  and 
which  is  more  liable  to  carry  silver  than  gold ; 
copper  pyrites  (chalcopyrite,  sulphuret  of  cop- 
per and  iron),  a  valued  source  of  the  precious 
metals,  and  which  is  composed  of  about  equal 
parts  of  copper,  iron,  and  sulphur ;  bornite 
(purple  copper  ore,  variegated  copper  ore,  va- 
riegated copper  pyrites,  erubescite,  "  horse- 
flesh "  ore,  sulphuret  of  copper  and  iron),  an 
ore  similar  to  the  preceding,  but  with  less 
iron;  gray  copper  ore  ("fahlerz,"  tetrahe- 
drite),  a  sulphide  of  copper  and  antimony  with 
smaller  and  varying  amounts  of  other  sulphu- 
rets  ;  and  finally,  all  other  and  rarer  sulphu- 
rets  with  copper  as  an  important  ingredient, 
such  as  Barnhardite,  Bournonite,  Carrollite, 
Covellite,  Harrisite,  Stromeyerite,  and  Ten- 
nantite. 

These  ores  can  be  treated  by  any  one  of  the 
five  methods  given  for  the  sulphuret  of  iron, 
and  which  I  repeat  here,  with  some  alterations 
in  the  proportions  of  the  ingredients  of  the 


300 


MANUAL    OF  ASSAYING. 


various  charges,  and,  for  the  sake  of  space,  in 
tabular  form. 

Even  these  charges  will  have  to  be  modi- 
fied more  or  less  to  suit  any  particular  sam- 
ple, for  it  may  be  a  mixture  of  two  or  more 
of  the  above-named  ores,  but  they  will  serve 
as  representative  methods.  Salt  cover  to  all, 
as  usual. 


METHOD 
A. 

METHOD 
B. 

METHOD 
C. 

METHOD 
D. 

METHOD 
E. 

Ore. 

i  A.T. 
30  grins. 
480  grains. 
Roasted. 

i  A.T. 
30  grms. 
480  grains. 

i  A.T. 
30  grms. 
480  grains. 

i  A.T. 
30  grms. 
480  grains. 

i  A.T. 
30  grms. 
480  grains. 

Bi-carb. 
Soda. 

4  A.  T. 

45  grms. 
720  grams. 

.  i^A.T. 
45  grms. 
720  grains. 

i|  A.  T. 

45  grms. 
720  grains. 

4A.T. 
45  grms. 
720  grains. 

3  A.  T. 

90  grms. 
i,  440  grains. 

Carb. 
Potash. 

\  A.  T. 

15  grms. 
240  grains. 

U.T. 

15  grms. 
240  grains. 

iA.T. 
15  grms. 
240  grains. 

iA.T. 

15  grms. 
240  grains. 

0 

Litharge. 

2  A.T. 

60  grms. 
960  grains. 

2  A.T. 

60  grms. 
960  grains. 

6  A.T. 

175  grms. 
2,880  grains. 

2  A.T. 
60  grms. 
960  grains. 

iA.T. 
15  grms. 
240  grains. 

Silica. 

i  A.T. 
30  grms. 
480  grains. 

i  A.T. 

30  grms. 
480  grains. 

2  A.T. 
60  grms. 
960  grains. 

i  A.T. 

30  grms. 
480  grains. 

i  A.T. 

30  grms. 
480  grains. 

Borax  glass. 

|A.t. 

6  grms. 
96  grains. 

i  A.  T. 
6  grms. 
96  grains. 

i  A.T. 
30  grms. 
480  grains. 

iA.T. 
6  grms. 
96  grains. 

iA.T. 

15  grms. 
240  grains. 

Charcoal. 

T8ff    grm. 
12^  grains. 

o 

After  fusion 
i  grm. 
15^  grains. 

0 

0 

Nitre. 

0 

if  A.  T. 

50  grms. 
770  grains. 

2!  A.T 

67  grms. 
i,  080  grains. 

0 

r<y  A.  T. 

9  grms. 
114  grains. 

Nails. 

0 

0 

o 

6 

6 

GOLD  AND   SILVER   ORES.  30! 

Copper  pyrites  —  that  is,  the  sulphurets  of 
iron  and  copper  partially  oxidized  —  should 
be  treated  like  the  unchanged  pyrites.  When 
entirely  converted  into  the  oxides  of  copper 
and  iron  use  Method  A  of  the  sulphuret  of 
copper  charge  given  above,  and  Aaron's 
charge  on  page  298. 

IV. OXIDES    OF    COPPER. 

The  oxides  of  copper  are  the  red  oxide 
(cuprite),  with  88.8  per  cent  copper,  and  the 
black  (melaconite,  tenorite),  with  79.8  per 
cent  of  that  metal.  As  oxidized  minerals 
there  are  the  hydrated  oxy-carbonates,  mala- 
chite (green  carbonate),  and  azurite  (blue 
carbonate),  with  57.4  and  55.3  per  cent  of 
copper  respectively. 

The  two  oxides  differ  chiefly  in  this,  that 
the  black  oxide  is  oxidizing,  i.e.,  giving  up  its 
oxygen  during  fusion,  while  the  other  does 
not  do  so.  Hence,  extra  reducing  agent 
must  be  added  to  the  former. 

Use  either  the  litharge  or  Aaron's  pro- 
cess. 


302  MANUAL   OF  ASSAYING. 

For  the  former,  make  up  the  charge  given 
as  Method  A  for  sulphurets  of  copper,  using 
-fa  grm.  (12^-  grains)  charcoal  for  the  black 
oxide,  and  ^  grm.  (7f  grains)  for  the  red. 

For  Aaron's  process,  use  the  charge  on 
page  298. 

Malachite,  azurite,  and  other  oxidized  ores 
containing  not  as  much  copper  as  the  above 
two  oxides,  will  need  but  the  regular  amount 
of  litharge  for  the  litharge  process  (i^  A.  T., 
45  grammes,  720  grains). 

Chrysocolla,  the  silicate  of  copper,  calls  for 
no  especial  remark,  save  only  that  the  charge 
will  not  require  quite  so  much  silica. 

V. GALENA. 

Galena  (galenite,  "pyrites  of  lead,"  sul- 
phuret  or  sulphide  of  lead)  is  so  frequently  a 
source  of  silver,  or,  at  least,  so  many  times 
associated  with  other  minerals  that  do  carry 
silver,  that  its  assay  is  often  called  for.  Some- 
times, although  not  often,  galena  is  rich  in 
gold  and  quite  free  from  silver ;  but  whether 


GOLD  AND   SILVER   ORES.  303 

auriferous  or  argentiferous,  it  makes  no  differ- 
ence in  the  manner  of  treatment 

The  silver  in  this  ore  varies  from  a  mere 
trace  to  as  high  as  $1,500  per  ton.  It  is 
claimed  that  when  galena  contains  over  o.  i 
per  cent  silver,  that  it  is  due  to  the  presence 
of  a  true  silver  mineral.  This  is  probably  so ; 
at  all  events,  one  can  often  pick  out  from  the 
cleavage  of  a  rich  specimen  particles  of  argen- 
tite  or  horn-silver. 

For  the  assay  treatment,  use  Method  B, 
p.  289,  with  the  litharge  -J-  part  (meaning  by  a 
part  i  A.  T.,  30  grammes  or  i  oz)  and  the 
nitre  -f$  of  a  part.  Or  Method  C,  with  i  part 
litharge  and  f  part  nitre.  Or,  finally,  Method 
D,  with  ^  part  litharge. 

An  approximate  assay  for  silver  in  galena 
can  be  made  by  cupelling  the  buttons  obtained 
in  the  lead  assay,  etc.,  and  making  the  proper 
calculations,  remembering  that  grammes  and 
grains,  and  not  A.  T.  weights,  are  used  in 
such  assays. 


CHAPTER    II. 
COPPER   ORES. 

OCCURRENCE. — Copper  is  found  both  native 
and  in  combination  with  many  elements, 
principally  with  sulphur  as  a  sulphide  or  sul- 
phuret,  with  oxygen  as  an  oxide,  and  with 
carbon,  hydrogen  and  oxygen  as  a  hydrated 
carbonate.  It  has  also  been  discovered  asso- 
ciated with  most  of  the  metals,  common  or 
rare. 

It  is  obtained  for  the  arts  and  manufactures 
mostly  from  the  following  ores  •. 

1.  Native  copper  (copper,  sometimes  accom- 

panied   by    silver),   when    pure,    100  per 
cent. 

2.  Cuprite  (red  oxide  of  copper),  with  88.8 

per  cent  copper. 

3.  Melaconite  (black  oxide  of  copper),  with 

79.8  per  cent  copper. 


COPPER   ORES.  305 


4.  Azurite  (blue  carbonate  of  copper),  with 

55.2  per  cent  copper. 

5.  Malachite    (green    carbonate    of   copper), 

with  57.4  per  cent  copper. 

6.  Chalcocite  (sulphide  of  copper),  with  79.8 

per  cent  copper. 

7.  Chalcopyrite  (sulphide  of  copper  and  iron), 

with  34.6  per  cent  copper. 

8.  Tetrahedrite    (gray    copper    ore),    copper 

variable,  normally  contains  about  38  per 
cent* 

ASSAY. — Of  the  many  dry  methods  for  the 
testing  of  copper  ores,  it  may  safely  be  said 
that  no  single  one  is  very  accurate.  The  vari- 
ous metallurgical  works  usually  have  pro- 
cesses or  modifications  of  processes  peculiar 
to  themselves,  but  which  are  always  more 
or  less  imperfect.  Many  of  these  processes 
are  complicated,  and  require  great  skill  with 
constant  practice. 

I  have  then  thought  it  best-to  specify  but 

*  See  appendix  for  more  extended  list  of  copper  minerals. 


306  MANUAL    OF  ASSAYING. 

three  assay  methods,  they  being  representa- 
tive ones. 

I.     METHOD    FOR    NATIVE    COPPER. 

(As  a  simple  mixture  of  rock  and  metallic 
copper.) 

Here  the  only  action  is  fusion. 

CHARGE. 

Ore 10  grammes  or  160  grains. 

Bi-carbonate  of  soda 20  "  "  320       " 

Carbonate  of  potash 5  "  "      80 

Borax  glass i  "  "      16 

Salt  and  charcoal  cover. 

Sample  ore  as  usual.  Mix  charge  and  pour 
in  "U"  crucible.  Put  cover  of  ^  inch  salt 
and  then  i  inch  of  wood  charcoal.  Cover  and 
heat  intensely  for  twenty  to  thirty  minutes. 
After  cooling,  break  crucible  and  clean  but- 
ton from  slag.  Divide  the  weight  of  button 
obtained  by  10  or  160,  and  multiply  this  result 
by  100  for  percentage  of  copper. 


COPPER    ORES.  307 


II.  METHOD    FOR    OXIDES    AND    CARBONATES    OF 

COPPER,    FREE    FROM    SULPHUR. 

Here  the  action  is  reducing,  followed  by 
the  collection  of  the  copper  globules  into  one 
button. 

CHARGE. 

Ore 10  grammes  or  160  grains. 

Black  flux  substitute 30  "          "    480       " 

Borax  glass 5  "          "      80 

Argol 2  "          "     32 

Salt  and  charcoal  cover. 

Use  a  "  U  "  crucible,  chalk-lined.  Cover, 
heat  gradually  for  twenty  minutes,  then 
increase  to  white-heat  for  forty  minutes.  Re- 
move, tap,  and  let  cool.  Results  approximate, 
the  error  augmenting  by  the  presence  of  other 
metals. 

III.  METHOD    FOR    SULPHIDES    OF   COPPER,  WITH 
ARSENIC,    ANTIMONY,     LEAD,     MERCURY,    ZINC, 

ETC. 

The  first  step,  concentration,  is  to  bring 
down  into  a  matte  all  the  copper,  and  to  get 
rid  of  obnoxious  lime  or  baryta  gangues. 


308  MANUAL   OF  ASSAYING. 

CHARGE. 
Ore,  according  to 

richness TO  to  30  grms.,  or  160  to  480  grains. 

*Iron  pyrites  . . . .    2    "     6       "        "      32   "     96       " 

Borax  glass 8    "  24       "        "    128   "  384       " 

Salt  cover. 

Mix  as  usual  and  transfer  to  crucible.  If 
lead  is  present,  put  in  a  couple  of  nails.  Fuse 
in  hot  fire,  remove  when  finished,  take  out 
nails  if  any  have  been  used,  cool,  break  away 
the  slag  from  the  matte,  and  treat  the  latter 
as  follows  : 

The  second  step,  roasting,  is  to  expel  the 
sulphur  and  the  volatile  metals,  arsenic,  anti- 
mony, zinc,  or  mercury,  converting  the  copper 
into  an  oxide.  Great  care  must  be  employed 
here,  hence  observe  the  directions  given  un- 
der Roasting  in  the  crucible  process  for  gold 
and  silver  ores,  pages  259  to  264,  using  coke 
in  place  of  charcoal,  and  no  silica. 

The  third  step  is  reduction,  or  bringing  the 
copper  from  its  state  of  oxide  to  that  of  a  metal. 

*  Containing  no  copper;  test  with  nitric  acid  and  ammonia.  If 
pyrites  is  in  the  ore  to  any  extent,  no  extra  amount  need  be  added. 


COPPER   ORES.  309 


CHARGE. 

Ore  (roasted) 30  grammes  or     480  grains. 

Black  flux  substitute 90         "  "1,440       " 

Borax  glass 15         "  "      240 

Lime  glass 7i       "  "      120 

Red  oxide  iron 3         "  "        48 

Salt  cover. 

(If  10  grammes  or  160  grains  ore  is  used, 
reduce  the  above  quantities  two-thirds.) 

Mix  the  ore,  oxide  iron,  and  one-third  the 
black  flux  substitute,  transfer  to  the  crucible, 
settle  down,  then  add  the  remaining  two-thirds 
of  the  black  flux  substitute,  the  borax  glass, 
lime  glass,  and  common  salt,  in  consecutive 
layers,  and  on  top  of  all  a  piece  of  coal  about 
the  size  of  a  hazel  nut.  Heat  slowly  at  first, 
then  intensely,  remove,  cool,  detach  button, 
etc.  If  it  seems  red  and  pure  and  is  malle- 
able, weigh  and  calculate  percentage.  If  not, 
then  there  comes  the  fourth  step,  purification 
or  refining. 

Two  large  cupels  are  welj  heated  in  the 
muffle;  into  each  a  piece  of  pure  lead  3 


3IO  MANUAL    OF  ASSAYING. 

grammes  or  48  grains  is  placed,  and  the 
muffle  is  closed.  When  the  leads  have  melt- 
ed, open  the  door,  and  into  one  cupel  drop 
the  impure  button,  into  the  other  a  piece  of 
pure  copper  of  the  same  weight.  Let  them 
remain  till  ''brightening"  occurs,  indicated  by 
a  peculiar  green  color.  As  soon  as  this  has 
happened,  cover  cupels  with  coke  or  coal 
dust,  take  out  and  cool  in  water.  The  loss 
the  pure  copper  has  sustained  in  cupellation 
is  supposed  to  be  the  same  as  the  button 
loses,  and  is  to  be  added  to  that  of  the  latter. 
Weigh  and  calculate  on  first  weight  of  ore 
taken.  Results  moderately  accurate. 

Read  Mitchell,  and  Bodeman  and  Kerl  on 
copper  assays.* 

*  Several  criticisms  have  been  made  upon  this  chapter  to  the 
effect  that  it  is  altogether  too  brief.  I  have  made  no  endeavor  to 
extend  it  in  this  revised  edition,  for  the  reasons  (one  of  which  has 
been  previously  stated)  that  the  fire  processes  are  not  accurate,  and 
that  they  are  gradually  being  substituted  everywhere  by  the  more 
exact  volumetric  and  electrolytic  methods  which  I  describe  in  full 
detail  in  the  appendix.  The  dry  assay  methods  described  are  as 
good  as  any,  and  cover  the  three  classes  of  copper  ores  common 
to  this  country,  i.e.,  free  metal,  oxidized,  and  sulphuretted  ores. 


CHAPTER    III. 

LEAD  ORES. 

OCCURRENCE. — Lead  is  very  rarely  found 
native  (that  is,  as  the  pure  metal),  but  occurs 
combined  with  various  elements,  as  antimony, 
arsenic,  carbon,  chlorine,  chromium,  molyb- 
denum, oxygen,  phosphorus,  selenium,  sul- 
phur, tellurium,  tungsten,  vanadium,  etc. 
Combinations  of  some  of  the  above  elements 
with  each  other  and  with  lead  exist,  either 
alone  or  associated  with  such  metals  as  cobalt, 
copper,  gold,  iron,  mercury,  nickel,  silver, 
zinc,  etc. 

Many  of  these  compounds  are  merely  min- 
eralogical  curiosities,  and  will  not  be  consid- 
ered here. 

The  important  workable  ores  are  the  fol- 
lowing : 

i.  Galenite  (galena,  sulphide  or  sulphuret  of 
lead),  when  piire  consist-ing  of  86.6 1  per 
cent  lead  and  13.39  Per  cent  sulphur. 


312  MANUAL    OF  ASSAYING. 

2.  Cerussite    (white    lead    ore,   carbonate    of 

lead),  containing  77.52  per  cent  lead. 

3.  Minium  (red  oxide),  with  90.80  per  cent 

lead.* 

ASSAY. — The  method    of   assaying   a  lead 
ore  depends  upon  the  nature  of  the  ore. 

I.     METHODS  FOR  GALENA. 

(Also  for  selenides,  sulphates,  and  for  galena 
containing  antimony  and  arsenic.) 

A,  By  Crucible  Fusion  in  Furnace. 

i.    With   bi-carbonate    of   soda  and    metallic 
iron. 

CHARGE. 

Ore 10  grammes,  or  160  grains. 

Bi-carbonate  of  soda 25          <l  "   400       " 

Carbonate  of  potash 10          "  "    160       " 

3  iron  nails  or 

3  loops  of  iron  wire. 

Salt  cover. 

Prepare  the  sample  according  to  the  direc- 
tions given  on  pp.  171-177. 

*  For  more  complete  list  of  lead  minerals  see  appendix. 


LEAD    ORES.  313 


Weigh  first  the  carbonates,  then  the  finely 
pulverized  ore,  and  mix  thoroughly  on  glazed 
paper. 

(Read  the  notes  on  the  "  Crucible  Assay  of 
Gold  and  Silver  Ores,"  pp.  243-244.) 

Brush  into  a  lettered  or  numbered  small 
sand  crucible  (size  "  U  "  of  Battersea  make), 
and  settle  contents  down. 

If  there  is  considerable  pyrites  in  the  ore, 
sprinkle  now  over  the  surface  of  the  charge 
one  gramme  of  finely  powdered  borax  glass. 

The  three  iron  nails  (eight-penny)  are  to 
be  held  together  by  their  heads  with  iron  wire 
(No.  1 6),  and  then  inserted,  points  down,  in 
the  crucible,  leaving  a  loop  of  the  wire  hang- 
ing over  the  edge  that  the  nails  may  be  easily 
and  quickly  withdrawn  when  the  operation  is 
concluded.  If  wire  only  is  used,  bend  a  piece 
of  the  No.  1 6,  about  six  inches  in  length,  in 
the  form  of  a  horse-shoe  with  a  loop  above, 
and  in  the  loop  hang  two  smaller  pieces  bent 
in  the  form  of  hair-pins  ;  let*  all  six  points  be 
about  on  a  level.  Insert  into  the  charge. 


3  1 4  MA NUAL   OF-  A  SSA  YING. 

Finally  pack  on  the  surface  of  the  charge 
and  around  the  nails  or  wire  one-half  inch  of 
dry  salt. 

Place  the  crucible  in  a  moderately  hot  fire, 
cover  and  surround  with  coke. 

This  process  will  require  twelve  to  four- 
teen minutes. 

When  fusion  is  complete,  take  off  the  cover, 
remove  crucible  from  fire,  then  by  means  of 
small  tongs  stir  the  nails  or  wire  loops  around 
in  the  molten  mass  once  or  twice,  and  while 
in  the  hot  fluid  tap  them  against  the  side  of 
the  crucible,  then  withdraw  them,  tap  gently 
the  crucible  and  cover.  All  this  should  be 
done  as  rapidly  as  possible. 

When  cold,  break  and  hammer  lead  into 
shape  as  usual. 

The  weight  of  the  button,  multiplied  by  ten 
(or  divided  by  sixteen  and  multiplied  by  ten), 
gives  the  ore's  percentage  of  metallic  lead. 

Tests  of  Good  Work. — After  fusion  the 
interior  of  the  crucible  should  be  smooth  and 
have  no  half-fused  portions  adhering  to  the 


LEAD   ORES.  315 


sides.     The  charge  should  be  well  settled  to 

o 

the  bottom  and  have  an  even  surface.  The 
slag  should  be  uniform  in  character,  and  of  a 
purplish-black  color.  The  lead  should  be  at 
the  bottom  in  one  button,  and  be  perfectly 
malleable.  A  glistening  button  indicates 
undecomposed  galena  ;  a  brittle  one  the  pres- 
ence of  antimony,  arsenic  or  iron. 

The  alkaline  carbonates  act  mainly  as 
fluxes,  but  a  portion  of  the  lead  they  convert 
into  a  double  sulphide  of  lead  and  soda  (or 
potash),  which  the  iron  desulphurizes,  form- 
ing sulphide  of  iron  and  metallic  lead. 

In  order  to  learn  the  proper  running  of  this 
lead  assay,  it  will  be  well  for  the  student  to 
perform  it  at  least  ten  times  on  the  same  ore. 

2.    With   black   flux  substitute    and    metallic 
iron. 

CHARGE, 

Ore 10  grammes  or  160  grains. 

Black  flux  substitute 35         "  "  560       " 

3  iron  nails  or 

3  loops  of  iron  wire. 

Salt  cover. 


3  1 6  MANUAL   OF  A SSA  YING. 

Treat  in  same  manner  as  for  the  first 
method.  Let  remain  in  fire  twelve  or  thirteen 
minutes. 

Add  one  gramme  or  fifteen  and  one-half 
grains  of  borax  glass  to  pyritic  ores. 

The  carbon  of  the  flour,  of  the  black  flux 
substitute  exerts  an  additional  reducing 
action. 

Perform  this  assay  a  number  of  times  for 
practice. 

The  remarks  given  under  the  first  method 
are  applicable  here. 

3.    With  cyanide  of  potash. 

CHARGE. 

Ore 10  grammes  or  160  grains. 

Cyanide  of  potash 30         "  "  480      " 

Salt  cover. 

Time  in  furnace,  about  fourteen  minutes. 
Cover  as  usual. 

In  this  process  the  sulphur  of  the  ore  unites 
with  the  cyanide  of  potash,  making  the  latter 
a  sulpho-cyanide. 


LEAD   ORES.  3  I  7 


Half-a-dozen  runnings  will  be  sufficient  for 
this  method. 

These  three  methods  can  be  performed 
with  satisfaction  in  Fletcher's  gas  furnace 
(p.  68). 

B.  By  Crucible  Fusion  in  Muffle. 
4.    With  bi-carbonate  of  soda  and  argol. 

CHARGE. 

Ore 10  grammes  or  160  grains. 

Bi-carbonate  of  soda 15  "  "  240  " 

Carbonate  of  potash 10  •*  "  160  " 

Argol 7  "  "  112  " 

Flour 5  "  "  80  " 

Borax  glass 3  "  "  48  " 

2  loops  of  iron  wire. 
Salt  cover. 

Mix  the  ore,  soda,  argol  and  flour,  and  pour 
into  a  small  sand  crucible  large  enough  to 
stand  in  the  muffle  used.  Sprinkle  over  the 
charge  the  fine  borax  glass,  insert  two  pieces 
of  iron  wire  bent  as  hair-pins,  and  tamp  down 
with  from  \  to  \  inch  dry  salt.  Use  no  cover. 

Have  the  muffle  at  a  bright  red  heat,  and 
place  the  crucible  or  crucibles  therein  ;  after 


3  I  8  MANUAL   OF  A  SSA  YING. 

about  ten  minutes  of  good  heat,  increase  the 
temperature  for  twenty-five  minutes  longer, 
when  the  contents  of  the  crucibles  should  be 
in  perfect  fusion. 

Take  out,  remove  wires,  tap,  and  let  stand 
covered  till  cool,  do  not  pour,  break,  hammer 
button,  etc. 

The  size  of  the  crucibles  used  will  depend 
upon  the  height  of  the  interior  of  the  muffle, 
and  the  fact  that  the  muffles  usually  employed 
are  small  very  often  either  necessitates  a 
smaller  charge,  or  renders  it  impossible  to  use 
this  process. 

For  this  work,  one  may  either  use  the  very 
small  crucibles  of  the  ordinary  form,  surround- 
ing each  crucible  with  a  little  cup  or  platform 
of  fire-clay  and  sand  mixed  up  with  borax 
water,  that  it  may  stand  securely  in  the  muffle, 
or  the  special  form  for  muffle  fusions  shown 
in  fig.  62.  The  latter  is  recommended. 

C.  By  Fusion  in  Scarifiers. 

This   is   a  modification   of   the  lead  assay 


LEAD   ORES.  319 


designed  to  be  used  where  the  muffles  are  not 
large  enough  to  admit  of  crucibles. 

It  is  simply  a  substitution  of  scorifiers  for 
crucibles,  using  the  same  charges  (reduced 
one-half  in  quantity)  as  for  crucible  work, 
and  employing  the  muffle. 

Half  the  third  charge  works  well,  thus  : 
5.    With  cyanide  of  potash. 

CHARGE. 

Ore 5  grammes  or    80  grains. 

Cyanide  of  potash 15  "240      " 

Salt  cover. 

For  a  "  J  "  Battersea  muffle,  employ  a  3^ 
inch  Battersea  scorifier.  Have  the  muffle  red 
hot,  introduce  scorifier,  cover  with  3^  inch 
circular  crucible  cover  ("G"  of  Battersea), 
heat  moderately  for  ten  minutes,  then  in- 
tensely for  twenty.  Remove  cover,  take  out 
scorifier,  do  not  pour  but  let  cool  covered, 
break,  and  shape  lead  button.  Multiply 
weight  by  twenty  (when  grammes  are  used), 
or  divide  it  by  eight  and  multiply  the  quotient 
by  ten  (when  grains  are  used)  for  percentage. 


320  MANUAL  OF  A  SSA  YING. 

Comparison  of  Processes. — The  cyanide  of 
potash  process  in  crucibles  gives  the  highest 
results,  the  buttons  are  clean  and  malleable, 
and  the  slags  almost  always  uniform.  I  have 
found  it  the  one  most  quickly  learned,  and  so, 
on  all  accounts,  I  give  it  the  preference. 

The    fourth    process    (crucible    in    muffle) 
comes  next  in  percentage  of  lead  obtained. 

The  second  process  (black  flux  substitute) 
ranges  next,  and  is  quite  satisfactory  to  work. 

Very  close  in  results  to  the  preceding,  is 
the  third  process  in  scorifiers  (No.  5,  half 
charge). 

The   first    process   (bi-carbonate  of   soda) 
gives  lower  results  than  any  of  the  others. 

A  method  with  ferrocyanide  of  potash,  that 
is  sometimes  used,  I  have  omitted  entirely,  on 
account  of  its  inaccuracy. 

II.     METHODS  FOR  OXIDES  AND  CARBONATES. 

(Cerussite,  minium,  etc.) 
By  crucible  fusion  in  or  out  of  muffle. 

6.    With  soda,  potash  and  argol. 


LEAD   ORES.  32! 


CHARGE. 

Ore 10  grammes  or  160  grains. 

Bi-carbonate  of  soda 15          "          "  240       " 

Carbonate  of  potash 5          "          "80       " 

Argol 5  "          "     80       " 

Salt  cover. 

Mix  as  usual,  and  transfer  to  small  crucible. 
Cover,  if  fusion  is  made  in  the  open  fire,  but 
not  if  the  muffle  is  used.  Heat  gradually  for 
about  fifteen  minutes,  then  somewhat  more 
strongly  till  fusion  ensues.  Take  out,  pour 
or  not,  as  desired.  Cover  if  left  in  crucible 
to  cool. 

Action  reducing — the  oxygen  of  the  ore  is 
seized  by  the  carbon  of  the  argol,  leaving 
metallic  lead. 

7.    With  soda,  argol  and  borax. 

Prepare  a  flux,  in  quantity,  of  the  following 
ingredients  : 

CHARGE. 

2  parts  bi-carbonate  of  soda. 
2  parts  argol. 

i  part  common  borax,  in  powder, 
i  part  flour. 


322  MANUAL  OF  ASSA  YING. 

Have  the  above  well  mixed,  then  sifted,  and 
keep  ready  for  use. 

Fill  about  two-thirds  full  a  so-called  "  5 
gramme"  crucible  (page  105),  with  the  above 
flux,  add  5  grammes,  or  80  grains,  of  the  ore, 
and  mix  in  crucible.  Put  in  muffle  without 
cover.  Keep  the  heat  as  low  as  possible, 
without  letting  it  get  too  cold. 

If  the  ore  shows  sulphurets,  put  in  a  nail  or 
two. 

If  the  ore  is  quite  calcic  or  barytic,  make 
the  borax  \\  parts  and  the  flour  f  of  a  part. 

For  ores  containing  much  manganese,  add 
to  flux  a  little  more  borax  and  flour. 

Cone  hiding  remarks. — At  the  best,  the  assay 
of  lead  ores  is  inaccurate,  mainly  on  account 
of  the  volatility  of  the  lead  itself,  though  in 
the  case  of  galenite  ores,  it  is  supposed  that 
the  galena  begins  to  sublime  before  the  de- 
composition is  effected. 

Also,  the  lead  button  is  liable  to  contain 
antimony,  iron,  and  zinc  from  the  ore,  or  iron 


LEAD  -ORES.  323 


from  the  nails,  wire,  or  iron  salts  employed  in 
the  assay. 

Try  then  to  avoid  an  unnecessarily  high 
heat,  remove  assays  as  soon  as  fusion  is  ob- 
tained, and  use  covers  as  much  as  possible. 

See  Mitchell,  5th  ed.,  pp.  443-477  inclusive. 


APPENDIX. 


SECTION    I. 
SPECIAL     METHODS. 

I.      ASSAYING    OF    THE    VARIOUS    MINERALS    CON- 
TAINED   IN    AN    ORE. 

It  is  sometimes  desirable  to  know  where  the 
gold  and  silver  are  located  in  an  ore,  that  is, 
which  minerals  carry  them  to  the  greater 
extent.  This  can  not  always  be  done,  for  the 
various  minerals  may  be  so  thoroughly  com- 
mingled that  separation  will  be  impossible. 
But  in  other  cases,  it  can  be  done  with  suc- 
cess. For  example,  an  ore  is  found  to  be 
made  up  of  three  distinct  minerals,  blende, 
galena  and  pyrites  in  a  quartz  gangue.  Weigh 
the  piece  selected,  and  crush  roughly  in  a 
mortar,  taking  care  not  to  lose  any,  and  pour 
out  on  a  clean  surface,  as  a  sheet  of  white 
paper.  With  a  pair  of  pincers  pick  out  such 
pieces  of  the  quartz  as  show  none  of  the  min- 


327 


328  MA  NUA  L    OF  A  SSA  YING. 

erals  mentioned,  and  reject  them.  Then  it 
will  be  comparatively  easy  to  put  aside,  in 
three  piles,  the  minerals,  each  quite  free  from 
the  other  two.  By  carefully  crushing  the 
remaining  mixed  pieces,  the  entire  lump  will 
finally  be  separated  into  its  three  component 
valuable  minerals  and  the  worthless  gangue. 

Weigh  each  lot,  and  assay    the    whole  of 
each  or  fractions  thereof. 

To  show  method  of  calculation,  I  give  the 
following 

EXAMPLE. 

Weight  of  sample  of  ore,  500  grammes, 
Which  was  composed  of: 

Pyrites,    40  grammes. 

Blende,    60          " 

Galena,  100 
Quartz  gangue,  300 

500  grammes. 

Percentage  of  pyrites  =-/Tr°irx  100  —     g 
"  "     blende=-$ftrXioo=    12 

"  "     galena  =i##X  100=   20 

-|f§-Xioo=   60 

100 


APPENDIX.  329 


Pyrites. — The  40  grms  gave  10  mgrms  gold — no  silver: 
^AX29.i66=o.58332=T5<y8ir  of  an  ounce  per  ton. 

Blende. —  rogrrns  gave  4  mgrms  silver — no  gold:  4X6 
=  24;  -^X  29. 166—1.39  oz-  silver  per  ton. 

Galena. — 20  grms  gave  160  mgrms  silver — trace  of  gold: 
160X5  =  800;  1^^X29.166—46.6  oz.  silver  per  ton. 

II.      ASSAYING    OF   ORES   CONTAINING   FREE   GOLD 
OR    FREE    SILVER. 

The  average  ore  does  not  carry  the  precious 
metals  in  the  free  state.  But  when  they  are 
present  in  such  form,  proceed  as  follows: 

Crush  the  sample  selected,  having  first 
weighed  it.  Pulverize  as  usual,  and  sift, 
using  the  box  sieve.  As  a  result  we  shall 
have  two  things,  the  finely  powdered  siftings 
below  and  more  or  less  free  metal  in  scales 
on  the  sieve. 

Weigh  the  scales,  and,  as  a  check,  the  sift- 
ings.  The  weight  of  the  latter  should  be  but 
a  trifle  less  than  the  difference  between  the 
original  weight  and  that  of  the  scales,  if  care 
has  been  taken  in  pulverizing. 

If  not  too  large  an  amount,  all  the  scales 


33  O  MANUAL   OF  ASS  A  YING. 

should  be  wrapped  in  pure  lead-foil,  and 
cupelled  directly.  If  quite  an  amount  be 
present,  simply  scorify  down  in  the  usual 
manner. 

Take  a  weighed  fraction  (one-half,  one- 
tenth,  one-twentieth,  as  the  case  may  be  )  of 
the  siftings,  and  assay  by  scorification  or  cru- 
cible process.  The  number  of  milligrammes 
gold  and  silver  obtained  are  each  to  be  multi- 
plied by  the  proper  fraction  to  ascertain  the 
amounts  present  in  the  entire  bulk  of  the 
siftings.  Add  the  gold  thus  calculated  to  be 
in  the  whole  of  the  siftings  to  the  amount 
found  to  be  in  the  scales,  and  the  same  with 
the  silver.  If  the  metal  is  all  free  gold  or  all 
free  silver,  the  calculations  are  still  simpler. 

The  following  example  explains  itself,  and 
illustrates  the  methods  of  calculation.  Fac- 
tors, depending  upon  the  relation  of  the  assay 
ton  of  29.166  grammes  to  the  amount  of  sam- 
ple taken,  may  or  may  not  be  used,  as  desired. 
If  a  fixed  quantity  of  ore,  as  100  grammes,  is 
always  taken,  the  factors  of  29.166-=-  100  — 


APPENDIX.  331 


0.29166,   or  of   100-^29.166  =  3.428,  will,   of 
course,  always  be  constant. 

Total  weight  of  sample  is 320.000  grammes 

Of  which  the  scales  weighed 260 

Hence  the  siftings  weighed 319. 740 

Factors 29.166-7-320=  0.09114, 

Or 320-5-29.166  =  10.97102. 

!2o8    mgrms.  silver, 
9.1  gold, 

217.1       "       total. 
208-5-320=0.65  ; 

then  0.65X29.166,     "I 

or  208X0.09114,      >  =18.95=07.  silver  per  ton  of  scales. 

or  208-7-10.97102,  J 
o.i -=-320=0.0284375  ; 
then  0.0284375X29.166,  "I 

or  9.1X0.09114,  >  =0.83=02.  gold  per  ton  of  scales. 

or  9.1-7-10.97102, 

51.75  mgrms.  silver, 


total. 


Siftings  :  319.74  grammes, 

30  grammes  produced  j   


[52.25 


51.75^-30=1.725;  i.725X3i9-74=55i.55i5;   551.5515-^320= 
1.7236; 

then  1.7236X29.166,  ] 

=  50.2=07.  silver  per  ton  of 
or  551.5515X0.09114,      }• 

siftings. 
or  551.5515-5-10.97102,    J 

1.50-5-30=0.05  ;  0.05X319.74  =  15-987, 
15.987-5-320=0.04996  ; 


332  MANUAL   OF  ASSAYING. 

then  0.04996X29.166,     "1 

or  15.987X0.09114,      V  =1.45=02.  gold  per  ton  of  siftings. 
or  15.987-7-10.97102,   J 

Silver  :  in  scales,      18.95  oz.,  @  $1.29  per  oz., =$24.44  per  ton. 
"  siftings,  50.20    "     "       "  "      =  64.75 

total,  69.15    "    "       "  "      —$89.19        " 

Gold:  in  scales,        0.83  oz.,  ©$20.67  per  oz.,=$i7.i5  per  ton. 
"  siftings,    1.45    "     "       "  "        =  29.97       " 


"         total,  2.28    "     "       "  "        =$47.12 

Total  value  of  scales $24.44-f$i7.i5=$  41.60  per  ton. 

Total  value  of  siftings  . .  .$64.75~|-$29.97=$  94.72        " 
Total  value  of  ore $89.i9+$47.i2=$i36.3i        " 

Check.* 

0.260  :  208: :  29.166  :  x,  o.26ox— 29.166X208=6066.928,  x 

=6066.928-5-0.260=23334.338,23334.338X1.29=30101.29. 

0.260:  9.1 ::  29.166  :  x;  o.26ox=29.i66X9. 1  =  265. 4106,   x 

=265.4106-^-0.260=1020.81,    1020.81X20.67=21100.14. 

30101 .29+21 100. 14=51201 .43. 

0.260  tons  scales,    @  $51,201.44  per  ton=$i3,3i2.37 
319.740     "    siftings,  "  94. 72  =  30.285.77 

320  tons  original  ore,  worth  $43,598.14  ;  or 

i  ton  is  worth  $136.24. 

*The  idea  of  the  check  or  verification  is  taken  from  C.  H. 
Aaron's  excellent  little  work  on  assaying,  and  consists  in  consid- 
ering the  ore  as  made  up  of  two  kinds  of  material,  assaying  each 
part  as  though  it  was  the  original  ore,  and  from  the  number  of 
imaginary  tons  of  each  kind,  calculating  the  actual  value  of  a  ton 
of  the  mixed  or  original  ore. 


APPENDIX.  333 


III.    ANALYSIS    OF    COPPER    ORES. 

The  wet  process  or  analysis  of  copper  ores 
is  so  much  more  accurate  than  the  dry  pro- 
cess or  assay,  that  it  should  always  be 
employed  when  practicable. 

As  in  the  assay  of  copper,  so  in  the  anal- 
ysis, there  are  many  methods,  here  included 
under  three  heads  ;  volumetry,  gravimetry 
and  electrolysis.  While  there  are  good  ways 
of  determination  among  the  first  two  classes, 
yet  I  prefer  one  in  the  third,  owing  to  its 
simplicity,  accuracy,  freedom  from  intricate 
calculation,  and  the  ease  with  which  it  can  be 
acquired. 

The  process  I  now  describe  is  known  as  the 
Luckow  method,  and  consists,  briefly  defined, 
in  dissolving  the  copper  out  of  its  combina- 
tions by  means  of  acids,  and  then  depositing 
it  as  the  metal  itself  upon  another  metal, 
platinum,  by  the  action  of  an  electric  current. 

It  makes  no  difference  whatever  in  this 
method,  how  the  copper  is  'originally  com- 
bined, whether  as  a  sulphide  or  in  a  mixture 


334  MANUAL   OF  ASSAYING. 

of  sulphides  of  other  metals,  an  oxide  or  car- 
bonate, a  matte  or  an  alloy ;  the  copper 
comes  out  as  metallic  copper  in  any  case.  * 

PROCESS. 

Prepare  the  sample  in  the  usual  manner, 
being  sure  to  use  a  loo-mesh  sieve.  Sample 
and  weigh  out  very  carefully  on  the  ore  scales, 
one  gramme,  if  the  ore  be  at  all  rich  (say 
above  20  per  cent),  or  five  grammes  if  it  be 
poor  in  copper  (below  20  per  cent). 

Brush  into  a  casserole,  i.e.,  a  porcelain 
evaporating  dish  with  a  handle  (fig.  75),  and 
cover  with  a  clock-glass  (fig.  68),  of  slightly 
larger  dimensions,  and  add  10  cubic  centi- 
metres of  pure  and  concentrated  nitric  acid, 
by  means  of  a  10  c.c.  pipette  (fig.  76). 

Now  place  the  casserole  either  on  a  sand- 
bath  (a  common  tin  plate  holding  some  dry 

*  If  accessible,  consult  a  very  interesting  paper,  entitled  "Com- 
parison of  Various  Methods  of  Copper  Analysis,"  by  Mr.  W.  E.  C. 
Eustis  of  Boston,  which  was  read  at  the  August,  1882,  meeting  in 
Colorado  of  the  American  Institute  of  Mining  Engineers,  and  is 
to  be  found  among  the  published  transactions  of  that  society. 


APPENDIX.  335 


sand),  or  on  a  piece  of  wire  gauze,  supporting 
either  on  a  ring-stand  (fig.  81),  and  heat  with 
a  Bunsen  burner  (fig.  83),  or  alcohol  lamp. 
Continue  this  heating  some  little  time,  then 
let  cool.  When  cold,  add,  from  another 
pipette,  5  c.c.  of  pure  and  concentrated  sul- 
phuric acid,  and  heat  to  boiling  till  no  more 
red  fumes  are  given  off,  but  in  their  stead 
dense  ivhite  vapors  are  delivered. 

The  red  fumes  are  from  the  nitric  acid,  the 
excess  of  which  we  wish  to  get  rid  of,  which 
is  done  by  means  of  the  sulphuric  acid,  and 
the  white  fumes  show  that  the  former  acid  is 
about  gone.  Let  the  casserole  stand  till  cold. 

Now  add  about  50  c.c.  of  distilled  water, 
stir  with  a  glass  stirring  rod,  heat,  and  let 
stand  till  any  undissolved  matters  have  set- 
tled to  the  bottom  of  the  casserole. 

While  this  is  doing,  prepare  for  filtering, 
that  is  the  separating  of  the  dissolved  copper 
(and  other  metals)  from  the  undissolved 
silica,  etc.  Place  in  proper  position  a  filter- 
stand  (fig,  87),  glass  funnel  (fig.  74),  and 


336  MANUAL   OF  ASSAYING. 


glass  beaker  (fig.  73).  The  filter-paper  is 
fitted  by  cutting  a  piece  in  a  square,  then 
folding  in  half,  diagonally,  and  then  into  quar- 
ters ;  it  will  form  a  triangular  figure,  and  if  the 
corners  are  cut  off  in  a  curved  line,  a  circle 
will  be  formed  on  spreading  out.  Upon  open- 
ing the  folded  paper  so  that  three  thicknesses 
come  on  one  side  and  one  on  the  other,  a 
filter  is  obtained,  which  is  placed  in  the  funnel 
and  wetted  by  means  of  the  wash-bottle  (fig. 
67).  This  useful  piece  of  apparatus  is  oper- 
ated by  simply  blowing  in  at  a  ;  a  fine  stream 
of  water  at  once  issues  from  b,  which  can  be 
directed  against  any  part  of  the  funnel. 

Filter  the  liquid  in  the  casserole  by  holding 
the  glass-rod  outside  the  lip  of  the  vessel, 
allowing  the  solution  to  run  down  the  rod 
into  the  funnel,  till  the  latter  is  nearly  full. 
Repeat  the  operation  until  nearly  all  the  solu- 
tion has  passed  through  the  funnel,  and  only 
the  sediment,  nearly  dry,  is  left  in  the  casserole. 
Examine  the  residue,  and  if  it  is  dark-colored, 
it  is  best  to  repeat  the  treatment  with  acids. 


APPENDIX.  337 


Generally,  however,  once  is  enough.  Finally 
wash  the  contents  of  the  casserole  into  the 
funnel,  which  fill  three  or  four  times  with 
water,  which  will  be  sufficient  to  wash  out  all 
the  copper  solution. 

The  residue  on  the  filter-paper  consists  of 
silica  and  other  substances  insoluble  in  the 
acids  used.  It  should  contain  no  copper. 

The  filtrate,  that  is  the  filtered  liquid,  con- 
tains the  copper  as  sulphate  (with  perhaps 
some  nitrate),  also  it  may  be,  iron,  lead,  etc., 
but  these  do  no  harm. 

The  next  thing  is  to  deposit  the  copper 
upon  platinum.  We  may  use  a  vessel  entirely 
of  platinum,  or  a  copper  dish  lined  with  plati- 
num, or  a  horseshoe  shaped  strip  of  platinum 
suspended  in  a  glass  beaker.  In  case  the 
operator  possesses  the  platinum  or  platinum- 
lined  dish,  clean  it  thoroughly  by  washing.  If 
it  is  a  new  vessel,  best  rinse  it  first  with  some 
solution  of  caustic  soda  or  potash  to  remove 
grease,  then  rub  it  gently  with  a  little  fine 
sand,  thus  giving  the  interior  a  surface  favor- 


MANUAL    OF  ASSAYING. 


able  for  deposition.  Be  sure  to  wash  off  all 
the  soda  or  potash  solution  and  sand,  then 
warm  till  it  is  perfectly  dry.  When  cool, 
weigh  carefully  on  the  ore  scales  and  note 
the  weight.  Pour  the  copper  solution  into 
the  platinum  dish,  using  the  glass-rod,  which 
rinse  off  with  water  into  the  dish;  finally  rinse 
out  the  beaker  with  a  little  water  into  the 
dish. 

We  now  have  a  weighed  dish  containing 
copper  in  solution  from  a  known  weight  of 
ore.  It  remains  to  connect  it  with  a  battery, 
which  latter  is  now  described. 


FIG.  93. 

Fig.  93  represents  two  cells  of  what  is  com- 
monly known  as  the  "  Bunsen  Carbon,"  which 


APPENDIX.  339 


form  a  battery  powerful  enough  for  our  pur- 
pose. A  quart  size  will  be  about  right.  It 
consists  of  a  glass  cell  or  jar  to  contain  the 
dilute  sulphuric  acid,  a  cylinder  of  cast-zinc, 
of  which  the  ends  do  not  quite  meet  ;  a  po- 
rous earthenware  cup,  to  hold  nitric  acid,  and 
a  rod  of  compressed  carbon. 

Prepare  a  mixture  of  strong  sulphuric  acid 
(ordinary  commercial)  and  water  in  the  pro- 
portion of  one  part  of  the  former  to  ten  of  the 
latter,  observing  the  precaution  of  pouring  the 
acid  into  the  water,  never  the  reverse.  Let 
the  zincs  stand  in  this  acid  solution  for  two  or 
three  minutes,  then  pour  over  them  a  little 
mercury,  and  rub  with  a  piece  of  soft  rag  tied 
around  a  stick,  till  the  entire  surface,  inner 
and  outer,  of  the  zincs,  is  coated  with  amal- 
gam. 

Put  each  cell  properly  together  and  fill  the 
glass  jars  with  the  sulphuric  acid  mixture,  just 
covering  the  tops  of  the  zincs.  Next,  nearly 
fill  the  porous  cells  with  concentrated  (com- 


34O  MANUAL   OF  ASSAYING. 

mercial)  nitric  acid.  *  See  that  the  binding 
screws  are  filed  bright,  also  the  connecting 
wires,  to  make  good  contact.  Arrange  appa- 
ratus as  follows  : 

The  zinc  of  the  first  cell  is  to  be  united 
with  the  platinum  dish  by  means  of  a  coil  of 
copper  wire  underneath  the  latter.  A  strip  of 
platinum  foil  (cleaned  with  potash  solution 
and  sand)  just  dips  into  the  solution  of  cop- 
per, and  is  connected  to  the  carbon  of  the 
second  cell  by  a  copper  wire.  Another  wire 
between  the  zinc  of  this  latter  cell  and  the 
carbon  of  the  first,  completes  the  circuit. 
Cover  the  dish  with  two  pieces  of  window- 
glass,  to  prevent  loss  by  spattering. 

The  copper  at  once  begins  to  line  the  inte- 
rior of  the  dish,  and  in  from  four  to  six  hours 
the  deposition  will  generally  be  complete. 
Time  is  often  gained  by  starting  the  action  at 
evening,  and  letting  it  run  a!4  night. 

Prove  the  complete  deposition  of  the  cop- 

*  A  bench  of  from  two  to  six  so-called  "gravity"  cells  will  do 
instead  of  the  pair  of  Bunsen  Carbons,  and  are  more  constant. 


APPENDIX.  341 


per  by  taking  one  drop  of  the  solution  and 
adding  to  it  one  drop  of  sulphuretted  hydro- 
gen water,  mixing  the  two  on  a  white  surface 
(cover  of  a  porcelain  capsule).  If  no  colora- 
tion ensues,  the  copper  has  all  been  thrown 
down  ;  if  a  black  discoloration  follows,  then 
there  is  still  copper  in  solution.  In  this  latter 
case,  continue  the  current  till  the  test  is 
negative. 

In  the  former  case,  pour  the  contents  of  the 
dish  into  a  clean  beaker,  rinse  the  dish,  the 
under  surfaces  of  the  glass  plates  and  the 
platinum  strip,  into  the  same  beaker.  On 
adding  to  the  contents  of  this  beaker  an 
excess  of  aqua  ammonia,  no  blue  coloration 
should  be  seen. 

Add  a  few  drops  of  alcohol  to  the  dish, 
rinse  around  and  drain  off.  Set  fire  to  the 
little  remaining  in  the  dish,  and  when  the  lat- 
ter is  cool,  weigh.  The  difference  between 
this  latter  weight  and  the  original  weight  of 
the  dish  is  metallic  copper.*  I  give  an 
example  : 


34 2  MANUAL    OF  ASSAYING. 

Weight  of  ore  taken  =i  gramme. 

GRAMMES. 

Weight  of  platinum  dish  and  copper=56.4o8 


copper  from  i  gramme^   0.749 
0.749  multiplied  by  100,  gives  74.9  per  cent 
of  metallic  copper  in  the  ore. 

As  before  mentioned,  instead  of  the  platinum 
dish,  which  is  quite  expensive,  a  glass  beaker 
can  be  used  to  contain  the  copper  solution. 
A  second  platinum  strip,  on  which  is  to  be 
deposited  the  copper,  must  be  used  here. 
Dip  this  in  the  beaker  and  connect  with  a 
zinc  element.  The  platinum  strip  in  straight 
form  connects  with  the  other  carbon  as  usual. 

If  the  copper  should  form  dark  colored  on 
the  platinum,  it  is  because  the  solution  is  too 
acid.  Nearly  neutralize  with  a  little  ammo- 
nia water,  to  counteract  its  bad  effect.  Too 
strong  a  current  should  also  be  avoided.  I 
have  given  this  process  well  in  detail,  but  it 
will  be  found  to  be  much  easier  learned  than 
described.  It  is  a  very  pretty  and  satisfactory 
method. 


APPENDIX.  343 


Volumetric  analysis  of  copper  ores. 

If  very  many  tests  of  copper  ores,  slags, 
mattes,  etc.,  are  to  be  made  daily,  it  will  be 
better  to  use  the  volumetric  process,  for  while 
it  is  not  quite  so  accurate  as  the  battery  pro- 
cess just  described,  it  is  much  more  rapid. 

My  thanks  are  hereby  tendered  to  Mr.  F. 
E.  Fielding,  of  Virginia  City,  Nev.,  for  many 
of  the  details  embodied  in  the  following  de- 
scription. 

Preparation  of  standard  solutions. 

Solution  of  cyanide  of  potassium. — Dissolve 
130.2  grammes  of  the  pure  salt  in  i  litre 
(1,000  c.c.)  of  distilled  water,  and  preserve 
from  the  light  in  a  glass-stoppered  bottle. 

Solution  of  metallic  copper.  --  Dissolve  i 
gramme  of  pure  copper  in  25  c.c.  nitric  acid 
of  32°  Beaume  (specific  gravity  1.26,  see  page 
211)  in  a  covered  beaker;  then  add  7  c.c.  of 
dilute  sulphuric  acid.  When  dissolved  and 
cool  add  caustic  ammonia,  or,  better  still,  am- 
monium carbonate,  in  slight  excess,  or  until 
the  blue  color  is  perceptible  throughout.  Di- 


344  MANUAL   OF  ASS  A  YING. 

lute,  when  cool,  with  distilled  water  to  exactly 
i  litre. 

Standardizing  the  cyanide  solution. —  Divide 
the  copper  solution  in  two  beakers,  so  that 
exactly  500  c.c.  shall  be  in  each  one,  repre- 
senting \  gramme  of  pure  copper.  Run  in 
the  cyanide  solution  from  a  burette  until  a 
faint  violet  color  is  produced.  Treat  the  sec- 
ond portion  in  the  same  manner,  and  take  the 
mean  of  the  two  results  as  the  standard. 
Multiply  each  result  by  two  to  bring  it  up  to 
the  basis  of  i  gramme  of  pure  copper,  repre- 
senting 100  per  cent.  The  cyanide  solution 
should  be  re-standardized  every  day  or  so. 

Preparation  of  the  ore  solution. 

Weigh  2  grammes  of  the  ore,  or  5  grammes 
if  very  poor  in  copper,  place  in  a  flask,  beaker, 
or  casserole,  moisten  with  about  7  c.c.  sul- 
phuric acid,  then  add  25  c.c.  of  nitric  acid. 
Digest  at  a  gentle  heat,  or  until  the  silicates 
look  white,  showing  that  all  the  metals  have 
been  extracted.  Boil  until  fumes  of  nitrous 
acid  are  no  longer  evolved,  cool,  and  add  am- 


APPENDIX.  345 


monia  or  carbonate  of  ammonia  in  slight  ex- 
cess ;  allow  the  solution  to  become  cool  and 
the  separated  flakes  of  brown-red  hydrated 
sesquioxide  of  iron  (if  present)  to  settle  to 
the  bottom  of  the  vessel.  If  necessary,  filter, 
and  wash  the  filter  paper  thoroughly. 

The  analysis. 

The  standard  solution  of  cyanide  is  now 
gradually  added  from  the  burette  (constantly 
stirring  the  copper  solution),  until  the  blue 
color  has  entirely  disappeared,  and  has  been 
replaced  by  a  faint  violet  tint,  corresponding 
as  nearly  as  possible  to  the  shade  produced  in 
titrating  the  solution  of  pure  copper  in  stand- 
ardizing the  cyanide  solution.  The  number  of 
c.c.  used  to  produce  this  is  now  read  off,  and 
from  it  the  percentage  of  copper  in  the  ore  is 
calculated.  A  single  example  will  illustrate 
the  simplicity  of  the  calculations. 

We  will  imagine  it  required  125  c.c.  of  the 
cyanide  solution  to  neutralize  the  i  gramme 
of  pure  copper  representing  ioo  per  cent, 


346  MANUAL    OF  ASS  A  YING. 


while  it  took  but  75  c.c.  for,  say,  2  grammes 
of  ore. 

125x2=250;  75-5-250=0.30;  0.30x100=30,  or  30  per  cent. 

Hence  the  rule  :  Multiply  the  number  of 
c.c.  of  cyanide  solution  used  for  the  pure  cop- 
per test  by  the  number  of  grammes  of  ore 
taken.  Divide  the  product  into  the  number 
of  c.c.  employed  on  the  ore  test,  and  the  quo- 
tient multiplied  by  100  will  give  the  percentage 
of  copper  in  the  ore. 

When  a  sulphuretted  ore  is  to  be  operated 
upon,  it  will,  in  a  majority  of  cases,  be  com- 
pletely oxidized  by  a  mixture  of  sulphuric 
and  nitric  acids,  but  should  any  globules  of 
sulphur  remain,  they  may  be  taken  out  after 
the  dilution  of  the  solution,  ignited,  and  the 
residue  dissolved  by  nitric  acid,  and  added  to 
the  original  solution.  (Or  such  ores  may  pre- 
viously be  roasted  in  the  manner  described  in 
the  section  on  gold  and  silver  ores.)  Some 
ores  are  best  attacked  by  aqua  regia  (i  part 
nitric  acid  to  three  parts  hydrochloric  acid). 

Owing  to  the  influence  of  varying  quanti- 


APPENDIX.  347 


ties  of  ammonia  and  of  ammonium  salts  upon 
the  decolorization  of  copper  solutions  by  po- 
tassium cyanide,  it  is  necessary  that  both  the 
test  solution  originally  prepared  and  the  vari- 
ous copper  solutions  subsequently  titrated 
should  contain,  as  nearly  as  possible,  equal 
amounts  of  ammonia. 

Interferences,  and  their  removal. 
Zinc,  nickel,  and  cobalt. — These,  if  present, 
render  the  analyses  unreliable,  so  that,  in  such 
cases,  the  copper  must  be  removed  by  precipi- 
tation from  its  solution.  This  may  be  done 
by  placing  a  piece  of  iron  or  zinc  in  the  solu- 
tion —  care  being  taken  that  nitric  acid  is  not 
present.  The  precipitated  metallic  copper 
thus  obtained  is,  after  removal  from  the  re- 
maining solution  of  interfering  metals,  dis- 
solved in  the  usual  manner.*  The  copper 
may  also  be  precipitated  as  sulphide  by  means 
of  sulphuretted  hydrogen  (see  page  150)  in 

*  Instead  of  re-dissolving,  it  can  be  drie'd  and  weighed  as  me- 
tallic copper,  giving  approximately  the  percentage  of  this  metal 
in  the  ore. 


348  MANUAL  OF  ASS  A  YING. 

acid  solution,  or  by  solution  of  sodium  thio- 
sulphate  (hyposulphite  of  soda),  and  the  sul- 
phide re-dissolved  and  estimated  as  described. 

Manganese  is  not  often  found  in  copper 
ores  in  sufficient  quantity  to  interfere.  If 
present,  it  may  be  removed  by  adding  to  the 
ammoniacal  solution  sodium  carbonate,  and 
a  few  c.c.  of  bromine  water,  and  boiling. 
When  cool  add  the  standard  solution  in  the 
usual  manner. 

Arsenic  does  not  interfere,  excepting  in  the 
presence  of  iron,  when  it  forms  an  arseniate 
soluble  in  ammonia,  and  gives  rise  to  a  brown- 
ish color  in  the  liquid.  It  may  be  removed 
by  adding  magnesium  sulphate  (epsom  salt) 
in  excess.  As  soon  as  a  precipitate  is  no 
longer  formed,  and  the  solution  has  recovered 
its  characteristic  blue  color,  run  in  the  stand- 
ard solution. 

Silver. — If  this  be  present  to  any  great  ex- 
tent, it  may  be  removed  by  adding  a  few 
drops  of  hydrochloric  acid  to  the  solution,  and 
filtering  before  the  addition  of  ammonia.  (Or 


APPENDIX. 


349 


the  hydrochloric  acid  may  be  added  at  same 
time  as  the  nitric  and  sulphuric  acids.) 

Iron. — This,  in  the  state  of  ferric  hydrate, 
does  not  interfere  chemically,  but  obscures 
changes  of  color  by  its  being  disseminated 
throughout  the  solution  ;  hence,  it  must  be 
allowed  to  settle  after  each  addition  of  the 
standard  solution.  It  may  be  kept  in  solu- 
tion by  means  of  tartaric  or  citric  acid. 

If  it  is  allowed  to  be  thrown  down  by  the 
ammonia,  whether  to  be  removed  by  filtration 
or  not,  it  should  be  borne  in  mind  that  in 
the  case  of  ores  very  rich  in  iron,  the  iron 
precipitate  will  retain  copper,  which  cannot 
be  dissolved  out  of  it  by  either  boiling  water 
or  ammoniacal  water.  Up  to  about  five  per 
cent  of  iron,  no  special  pains  need  be  taken, 
but  above  that  amount,  the  copper  ought  to 
be  first  removed  from  the  solution  by  sul- 
phuretted hydrogen,  then  dissolved  as  usual. 

Lead,  bismuth,  antimony,  and  magnesia  do 
not  interfere. 

Lime  in  large  quantity  tends  to  confuse  the 


3  5 O  MANUAL    OF  A  SSA  YING. 

results  ;  it  may  be  removed  by  addition  of 
oxalate  of  ammonia. 

The  preceding  statements  regarding  inter- 
ferences are  well  borne  out  by  a  series  of  ex- 
periments carried  on  by  Messrs.  Torrey  and 
Eaton,  New  York,  and  described  in  the  En- 
gineering and  Mining  Journal,  New  York, 
May  9,  June  9  and  27,  1885.  The  results, 
in  brief,  were  as  follows : 

Zinc:  3  per  cent  caused  an  (apparent)  in- 
crease of  \  per  cent  copper. 

Arsenic:  From  5  to  15  per  cent  did  no  harm. 

Silver :  25  per  cent  caused  an  error  of 
only  Ta¥  per  cent  copper. 

Iron:  30  per  cent  caused  a  loss  of  3.71  per 
cent  copper. 

Lead :  From  5  to  40  per  cent  had  no  in- 
jurious effect. 

Bismuth :  20  per  cent  allowed  the  same 
approximation  as  the  silver. 

Consult  the  above  article,  also  "  On  the 
Volumetric  Determination  of  Copper  by 
Means  of  Potassic  Cyanide,"  by  J.  J.  and  C. 


APPENDIX.  351 


Beringer,  Chemical  News,  Vol.  XLVIII,  No. 
1,241,  Sept.  7,  1883,  pp.  111-113,  and  Sutton 
and  Hart  on  volumetric  analysis. 

IV.    AMALGAMATION    ASSAY    OR    LABORATORY 

MILL    RUN. 
By  M.  G.  NIXON,  M.E. 

The  wet  copper  assay  bears  somewhat  the 
relation  to  the  fire  copper  assay  that  the  fire 
gold  assay  does  to  the  amalgamation  gold 
assay. 

In  a  certain  sense,  no  one  cares  to  know  the 
ultimate  amount  of  metal  that  an  ore  contains. 
What  is  desired  in  practice,  is  the  yield  under 
the  most  skilful  treatment,  and  this  informa- 
tion is  approximately  obtained  by  fire  for 
copper,  and  the  amalgamation  process  for 
gold. 

There  are  those  so  practised  in  "panning," 
that  from  a  "panful"  of  "pulp"  they  can 
very  closely  guess  the  yield  by  the  number  of 
"colors"  and  their  size.  Of  course  this 
method  is  not  very  popular,  nor  can  it  ever  be. 


352  MANUAL    OF  ASSAYING. 

Something  more  a  matter  of  weighing,  and 
less  a  matter  of  judgment  and  practice  is 
required. 

The  amalgamation  assay  in  its  simplest 
form  consists  in  "panning"  a  weighed  amount 
of  "  pulp  "  with  few  or  many  drops  of  mercury, 
accordingly  as  the  ore  is  poor. or  rich.  The 
tailings  are  washed  out  as  clean  as  may  be, 
the  pan  is  then  placed  over  a  fire  to  dry  and 
then  what  remains  of  dirt  and  dust  is  blown 
out  with  the  breath ;  the  pan  is  again  placed 
over  the  fire  and  the  mercury  volatilized,  leav- 
ing the  gold  ("retort")  ready  for  weighing. 
This  process  is  quite  largely  followed  by  pros- 
pectors in  some  of  our  free-gold  districts. 

An  improvement  on  the  method  just  de- 
scribed consists  in  grinding  the  pulverized  ore 
in  a  large  iron  mortar  with  which  water  and 
mercury  are  introduced,  with  the  pestle. 
When  the  grinding  is  complete,  the  whole  is 
washed  into  a  pan  to  be  collected  and  finished 
as  before. 

These  methods  are  not  recommended,  but 


APPENDIX.  353 


may  be  resorted  to  when  other  apparatus  can 
not  be  obtained. 

The  third  method  consists  in  grinding  say 
ten  or  twenty  pounds  of  ore  in  a  laboratory 
"arrastre"  by  hand  two  hours  or  more,  or, 
where  possible,  by  power  half  as  long.  It  is 
well  to  pass  the  ore  through  a  4O-mesh  sieve 
before  placing  it  in  the  "  arrastre."  From 
two  to  four  ounces  of  mercury  are  then 
squeezed  through  a  piece  of  chamois  skin,  or 
blown  through  a  tube  the  end  of  which  is 
drawn  out  so  as  to  make  a  pin-hole  exit. 
Having  put  the  pulp  and  mercury  into  the 
"  arrastre  "  mortar,  a  piece  of  potassium  cya- 
nide as  large  as  the  end  of  one's  little  ringer 
is  dropped  in,  the  grinder  adjusted,  enough 
water  added  to  cover  the  ore,  and  the  grind- 
ing performed.  After  it  is  finished,  the 
grinder  is  first  washed  off  into  a  collecting 
pan,  then  the  mortar  with  its  contents  is 
treated  in  the  same  manner.  The  best  way 
to  collect  the  amalgam  is  to  'hold  the  pan 
under  a  running  stream  or  water  faucet,  and 


354  MANUAL   OF  ASSAYING. 

very  gently  to  stir  it  with  the  hand.  The 
amalgam  is  then  placed  in  chamois  skin  and 
squeezed  so  as  to  get  rid  of  as  much  mercury 
as  possible. 

The  residue  is  next  placed  in  a  small  iron 
retort,  and  what  remains,  of  the  mercury  is 
driven  off  by  heat  gradually  increased.  Of 
course,  for  reasons  of  economy,  it  is  well  to 
condense  the  mercury.;  it  may  then  be  sold  to 
mills  or  others,  but  neither  that  portion  con- 
densed nor  that  squeezed  through  the  chamois 
should  be  used  over  again,  since  it  is  almost 
impossible  to  get  rid  of  the  last  traces  of 
gold.  The  "  retort "  is  then  to  be  scorified, 
cupelled,  inquarted,  etc.,  etc.* 

The  writer  has  saved  93  per  cent  of  the  fire 

*An  amalgam  obtained  as  a  result  from  either  the  preceding 
method,  from  panning  with  mercury,  or  from  any  other  process, 
can  be  treated  in  the  following  manner,  provided  it  is  not  in  too 
great  quantity. 

Into  a  new  scorifier  (say  2^  inches  in  diameter)  introduce  the 
amalgam  after  it  has  been  separated  from  the  free  mercury  by 
squeezing  in  a  piece  of  chamois  skin.  On  top  of  the  scorifier 
place  another  of  same  size,  inverted,  having  first  bored  through  it 
a  hole  about  l/fa  inch  in  diameter.  By  rubbing  down  a  little  the 
tops  of  the  scorifiers,  and  painting  their  edges  with  a  thick  wash 


APPENDIX.  355 


assay  on  the  same  ore  that  a  mill  at  the 
time  under  his  superintendence  returned  89 
per  cent. 

V.     PAN    TEST    FOR    GOLD. 
("PANNING.") 

The  estimation  of  gold  in  ores  in  which  the 
metal  is  in  the  free  state  is  unreliable  by 

of  ground  chalk  and  water,  all  danger  of  loss  of  amalgam  by  its 
spirting  through  at  the  sides,  is  avoided. 

Heat  in  muffle  or  furnace  till  the  mercury  has  been  driven  off 
in  vapor  through  the  fine  opening  above,  take  out,  let  cool  and 
remove  the  upper  scorifier. 

Now  put  the  chamois  skin  on  top  of  the  residue  in  the  scorifier 
and  burn  to  ashes  in  muffle  or  furnace,  remove  a  second  time  and 
cool. 

Finally  mix  the  residue  and  ashes  with  granulated  lead  and 
scorify.  Re-scorify  with  more  lead  if  the  resulting  button  is  brit- 
tle. Cupel  in  the  usual  manner  and  treat  the  bead  obtained  as 
gold  bullion. 

If  it  is  not  thought  worth  while  to  save  the  mercury,  the  fluid 
amalgam  can  be  treated  directly  as  described  without  first  squeez- 
ing through  a  chamois  skin,  in  which  case  the  accompanying  step 
of  burning  the  latter,  etc.,  is  dispensed  with.  Heat  very  gradually. 
Even  with  this  apparatus  the  mercury  can  be  saved  by  attaching 
to  the  upper  scorifier  a  small  iron  tube  which  bends  over  and  dips 
into  water. 

The  advantages  of  the  above  method  are  that  it  is  simple,  easy 
to  operate,  and  that  all  the  work  (up  to  the  cupellation)  is  done  in 
one  vessel,  and  so  any  liability  to  loss  of  gold  in  transferring  from 
a  retort,  etc.,  is  done  away  with.  Furthermore,  working  with 
small  quantities  of  amalgam,  in  even  the  smallest  retort  obtainable, 
is  unsatisfactory. — W.  L.  B. 


356  MANUAL   OF  ASSAYING. 

either  the  crucible  or  scorification  process, 
owing  to  the  impossibility  of  securing  an 
average  sample. 

The  ore,  for  supposition,  may  be  of  such 
value  that  even  when  put  through  a  loo-mesh 
sieve  one  flake  that  would  go  through  such 
a  mesh  could  represent  the  amount  of  gold 
in  two  assay  tons. 

If  then  of  two  assay  tons  of  ore  of  the  above 
character,  one  is  taken,  it  must  run  either 
nothing  or  double  the  true  value  of  the  ore. 

Again,  on  low  grade  ores  and  with  the 
charge  most  convenient  to  employ,  the  result 
or  weighable  button  is  so  small  that  its  esti- 
mation is  liable  to  error. 

Many  ores  containing  small  quantities  of 
gold  are  frequently  profitable  to  work,  as  in 
the  case  of  placers  and  of  large  quartz  ledges 
where  the  rock  is  soft  and  gold  free.  In  such 
cases  the  assay  report  based  upon  the  small 
quantity  of  ore  used  in  the  scorification,  or 
even  in  the  crucible  assay,  is  unsatisfactory  for 
this  and  the  previous  reasons. 


APPENDIX.  357 


Here,  then,  we  resort  to  the  pan  test,  for  by 
it  we  can  treat  large  amounts  of  ore,  and  the 
greater  the  quantity  operated  upon  the  more 
reliable  the  result. 

The  pan  test  is  a  process  of  concentration 
(doing  on  a  small  scale  that  which  concentra- 
tors effect  on  the  large),  the  product  being 
either  gold  particles,  or  gold  sulphurets,  iron, 
sand,  etc.,  depending  on  how  far  the  process 
is  carried. 

The  pan  itself  is  a  Russia  sheet  iron  vessel 
of  a  shallow  truncated  conical  shape  (diameter 
about  i6J  inches).  That  form  sold  by  min- 
ing outfit  establishments  has  been  found 
most  useful  in  practical  operations.  A  round 
shallow  wooden  dish  with  its  bottom  sloping 
to  a  point,  and  technically  known  as  a 
"  Batea,"  is  a  useful  modification  (fig.  48 
of  Atwood  ;  size  of  batea  :  diameter,  1 7  inches  ; 
depth,  i  finches;  thickness,  f  inch;  angle  of 
sides,  12°;  material,  Honduras  mahogany). 
Each  person  will  exercise  his  own  choice  after 
learning  the  operation.  After  the  requisite 


MANUAL    OF  ASSAYING. 


skill  has  been  acquired,  a  pan  can  be  extem- 
porized from  almost  any  kind  of  dish,  or  a 
section  of  bullock's  horn  or  an  iron  spoon 
may  serve  as  substitutes. 

The  requisite  amount  of  ore  from  100  to 
500  assay  tons  (5  to  25  pounds,  or  in  French 
weights  3  to  15  kilos),  depending  upon  its 
richness,  is  sampled,  crushed  and  pulverized 
as  directed  in  the  chapter  on  gold  and  silver 
ore.  The  pulverization,  however,  need  be 
carried  no  finer  than  to  cause  the  ore  to  pass 
through  a  40,  50  or  60  mesh  sieve  (the  latter 
preferred).  Weigh  now  the  ore  and  put  in 
the  pan,  which  latter  must  be  free  from 
grease.  Moisten  and  let  it  stand  for  a  few 
moments  in  order  that  particles  may  not  float 
off  when  the  pan  is  put  in  water. 

When  wet,  the  whole  pan  and  ore  is  gently 
sunk  below  the  surface  of  a  tank  of  water  (a 
common  wash  tub  will  do  nicely  in  the  labora- 
tory). A  peculiar  oscillatory  motion  or  side 
vibration  is  commenced,  though  not  enough 
to  throw  any  particles  of  ore  over  the  edges 


APPENDIX. 


359 


of  the  pan.  The  object  of  this  is  to  settle  the 
heavier  particles  (the  free  gold,  heavy  miner- 
als, black  sand,  etc.),  and  have  nothing  on  the 
surface  but  rock  or  quartz  ;  a  little  experience 
will  teach  the  point.  Then  slightly  incline 
the  pan,  and  so  wash  it  around  as  to  carry  the 
surface  rock  over  the  edge  ;  only  a  little  at  a 
time,  however. 

Level  the  pan  and  resettle  as  at  first ;  again 
incline  and  wash  more  over  the  edge.  Keep 
up  this  operation,  gradually  getting  more  and 
more  rock  over  the  edge,  and  becoming  more 
careful  and  washing  more  delicately  as  the 
process  continues. 

Toward  the  end  of  the  operation,  that  is, 
when  the  rock  is  nearly  gone,  be  careful  to 
keep  the  ore  under  the  surface  of  the  water, 
as  the  gold  might  otherwise  become  dry  and 
float  off.  Also  make  no  sudden  or  unusual 
lurch,  or  the  whole  result  may  go  off  the  pan. 
The  above  manipulation  is  far  more  difficult 
to  describe  than  to  perform  after  having  once 
been  acquired.  Dry  the  residue. 


360  MA NUAL    OF  A  SSA  YING. 

If  gold  alone  is  obtained,  that  is,  gold  (or 
gold  and  silver)  free  from  sulphurets,  etc.,  it 
must  be  treated  as  an  alloy,  weighed,  parted 
and  weighed  again,  or  cupelled  with  lead, 
weighed,  parted  and  weighed  ;  in  both  cases 
giving  gold  and  silver. 

If  the  panning  is  not  carried  to  such  a  point 
as  to  get  rid  of  all  the  rock,  the  concentration 
is  all  scorified  with  test  lead  (or  run  down  in 
a  crucible),  cupelled,  parted  and  weighed. 
In  the  case  of  an  ore  supposed  to  carry  aurif- 
erous sulphurets  it  should  be  panned  so  far 
as  can  safely  be  done  without  losing  metallif- 
erous particles  and  the  concentration  treated 
as  above  described. 

If  the  ore  is  quite  poor,  or  a  large  quantity 
is  desired  to  be  worked,  the  panning  can  be 
carried  on  roughly  and  the  successive  con- 
centrations finally  panned  together. 

The  results  are  based  upon  the  amount  of 
ore  taken  in  the  pan.  If  much  of  this  work 
was  to  be  done,  a  set  of  weights  from  500 
A.  T.  down  (approximately  accurate)  would 


APPENDIX. 


be  very  convenient  and  save  calculation.  The 
result  would  be  as  many  times  the  number  of 
ounces  contained  in  the  ore  as  the  quantity 
of  ore  was  more  than  one  assay  ton. 

For  example,  the  ore  was  supposed  to  be 
very  poor  and  therefore  : 

500  A.  T.  were  taken. 

Bead  weighed  50  mgrms. 

/.  500  A.  T.  :  i  A.  T.  : :  50  mgrms.  :  y1^  mgrm., 
or  the  ore  ran  y1^  oz.  Troy  per  ton. 

If  100  A.  T.  had  been  taken  and  the  same 
weight  bead  obtained,  we  would  have  : 

100  A.  T.  :  i  A.  T.  ::  50  mgrms.  :  -£  mgrm., 
or  the  ore  would  run  -J  oz.  Troy  per  ton. 

As  an  example  of  the  calculation  required 
^v^thout  the  large  assay  ton  weights,  I  give 
the  following  : 

Weight  of  panful  of  ore,  2^  kilogrammes  =  2, 250,000 

milligrammes. 
Weight  of  bead  obtained,  gold  20  mgrs.,  silver  50  mgrs., 

then    2,25o,ooomgrms       29166 
20  mgrms.  x 

,     2,250,000  mgrms.       20166 
and  -  -  : :  —   —  X  =  ATT  oz. 

50  mgrms.  x 

The  free  gold  can   be  separated  from  the 


362  MANUAL    OF  ASS  A  YING. 

sulphurets  (if  it  be  desired  to  determine  how 
much  of  the  gold  is  "  free  "  and  how  much  in 
the  "sulphurets")  by  washing  in  an  amal- 
gamated pan.  Such  a  vessel  may  be  simply 
made  by  bending  a  piece  of  thin  silver-plated 
copper  (about  6  inches  by  12  inches)  so  as  to 
form  curved  edges  on  three  sides,  the  silvered 
sides  in.  The  side  not  turned  up  is  one  of 
the  narrow  ends.  A  little  mercury  (free  from 
gold  and  silver)  will  quickly  amalgamate  the 
interior,  and  if  the  ore  is  washed  carefully 
over  this,  most  of  the  free  gold  will  become 
amalgamated  and  stick  to  the  pan.  A  piece 
of  chamois  skin  made  into  a  rubber  will  push 
the  gold,  which  can  be  seen  as  little  specks  of 
amalgam,  to  the  open  edge  of  the  pan  and 
into  a  crucible.  The  mercury  can  be  driven 
from  the  gold  by  heat. 

No  investigation  has  been  made  to  deter- 
mine if  any  silver  is  carried  by  the  mercury 
to  the  assay  from  the  pan,  but  if  such  be  the 
fact,  the  result  is  still  accurate  for  gold.  If 
carefully  performed  the  results  ought  to  be 


APPENDIX.  36, 


above  the  yield  from  a  stamp-mill  with  amal- 
gamated plates. 

A  more  common  test  than  with  the  above 
silver-plated  amalgamated  copper  pan,  is,  after 
having  panned  down,  to  drop  a  few  globules 
of  clean  "quicksilver"  (i.e.,  mercury)  into 
the  pan  and  a  little  cyanide  of  potassium  (to 
keep  the  mercury  clean).  Work  up  with  a 
spatula  till  the  mercury  has  taken  up  the  free 
gold,  then  collect,  and  run  off  the  mercury. 
Clean  it  and  dissolve  in  nitric  acid  (for  the 
gold  only)  or  drive  off  the  mercury  in  the 
muffle,  weigh  the  residue  of  gold  and  silver, 
part  and  weigh  gold. 

The  residue  in  the  pan  should  then  be 
assayed  and  the  gold  and  silver  (actual 
weight)  determined.  Suppose 

Original  weight  of  ore. 2^  kilos. 

Gold  and  silver  after  retorting 35  mgrms. 

Gold  after  parting 15       " 

Hence  silver , 20  mgrms. 

Gold  in  sulphurets 50  mgrms. 

Silver  "  90      " 


364  MANUAL    OF  ASSAYING. 

Then  we  have  : 


Free  gold  -j^^  oz.  per  ton  of  original  ore. 
Silver  in  free  gold  j2/^  oz.  per  ton  of  original 

ore. 
Gold  in  sulphurets  -ffa  oz.  per  ton  of  original 

ore. 
Silver  in  sulphurets  iTV6o  oz-  Per  ton  °f  origi- 

nal ore. 

Total  gold  y8^  oz.  per  ton  of  original  ore. 
Total  silver  lyW  oz-  Per  ton  °f  original  ore. 

There  is  a  certain  loss  in  panning,  hence 
the  results  are  not  analytically  accurate,  but 
are  close  indications  of  the  practical  result  of 
the  working  of  gold  ores  in  a  mill  with  copper 
plates.* 

VI.     CHLORINATION    ASSAY    OF    GOLD    ORES. 

If  gold  exists  free  in  the  gangue,  that  is, 
not  combined  with  sulphur,  arsenic  or  tellu- 
rium, it  can  be  chlorinated  directly  without 
roasting. 

*  For  the  information  comprised  in  the  above  article  I  am 
largely  indebted  to  Mr.  S.  A.  Reed  of  Irvvin,  Col.,  and  Mr.  Ray 
G.  Coates  of  Chicago, 


APPENDIX.  365 


But  sulphurets,  arseniurets  or  tellurides 
must  be  first  roasted  and  thoroughly  at  that. 

The  chlorination  can  be  done  in  the  labora- 
tory on  either  a  large  or  moderately  large 
scale.  For  the  former,  operating  say  on  20 
pounds  (yihr  °f  a  ton)>  consult  the  section  in 
Kustel,  entitled  "  Extraction  of  Gold  from 
Sulphurets,  Arseniurets  or  Quartz,  by  Chlor- 
ination," pp.  136-139. 

For  the  latter  grind  up  5  to  8  ounces  (or  5 
to  10  A.  T.),  and,  if  necessary,  roast  in  the 
usual  manner.  Use  a  frying  pan  for  this 
purpose,  and  see  that  the  sulphur  is  entirely 
driven  out  so  that  no  smell  (as  of  a  burning 
match)  is  perceptible  at  the  finish.  Cool, 
grind  in  an  iron  mortar,  and  re-roast  at  a  red 
heat. 

When  cold,  reserve  i  A.  T.  of  the  ore  for 
regular  assay;  the  remainder  is  to  be  chlori- 
nated in  the  apparatus  herewith  described.  It 
consists  of  a  flask,  provided  with  a  funnel  tube 
for  acid  supply  and  delivery  tube  for  the  chlor- 
ine gas  generated.  The  latter  tube  dips  into 


366  MANUAL    OF  ASSAYING. 

a  wash  bottle  containing  water  to  wash  the 
gas.  From  the  latter  the  gas  passes  up  into  a 
separatory  funnel  containing  the  ore.  The 
exit  tube  from  the  funnel  may  pass  into  a  flue 
or  the  open  air,  or  into  a  cylinder  holding 
shavings  moistened  with  alcohol. 

Place  in  the  flask  a  mixture  of  3  parts  of 
black  oxide  of  manganese,  4  parts  of  common 
salt,  and  4^  parts  of  water,  all  well  mixed. 

Place  the  ore,  which  has  been  dampened 
with  water,  in  the  separatory  funnel,  having 
put  in  at  the  bottom  a  very  little  cotton  to 
prevent  the  fine  ore  from  stopping  the  pas- 
sage of  the  gas. 

Having  now  made  all  ready,  pour  down 
through  the  funnel  tube  7^  parts  of  sulphuric 
acid  at  intervals.  After  a  time  the  flask  is  to 
be  gently  heated,  that  all  the  chlorine  may  be 
driven  off. 

Run  the  operation  for  about  two  hours, 
then  disconnect  the  flask  and  let  the  funnel 
stand  over  night.  Finally  take  out  the  upper 


APPENDIX.  367 


cork  and  wash  out  the  chloride  of  gold  with 
distilled  water. 

To  the  solution  in  a  beaker  or  tumbler  add 
a  few  drops  of  hydrochloric  (muriatic)  acid, 
then  some  solution  in  water  of  sulphate  of 
iron  (green  vitriol  or  copperas),  stir  with  a 
glass  rod,  warm  and  let  stand  undisturbed 
until  all  the  gold  has  been  thrown  down  to 
the  bottom  and  the  liquid  above  is  perfectly 
clear.  Half  of  this  liquid  is  drawn  off  with  a 
syphon,  the  remainder  containing  the  gold  is 
filtered  as  usual,  washing  with  warm  water. 
Dry  the  filter,  burn,  scorify  ashes  and  cupel, 
or  cupel  directly  with  sheet  lead,  weigh,  etc. 
Compare  result  with  unchlorinated  sample. 
Consult  Kustel  as  above,  and  Aaron's  "  Leach- 
ing Gold  and  Silver  Ores,"  p.  90,  on  the  ''Work- 
ing Test." 

VII.    CHLORINATION    TEST    FOR    SILVER. 

In  smelting-works  it  is  often  necessary  to 
test  ores  that  have  been  subjected  to  chlorid- 
izing  roasting,  to  ascertain  the  amounts  of 
chloride  of  silver  contained  in  them.  Two 
assays  are  made  of  each  ore. 


368  MANUAL    OF  ASSAYING. 

Several  pounds  of  the  ore  are  taken  from 
various  portions  of  the  entire  lot,  well  mixed 
and  sifted.  From  this,  weigh  out  two  charges 
of  _i_  A.  T.  Scorify  and  cupel  one  charge  in 
the  usual  manner. 

The  other  charge  is  brushed  into  a  filter 
paper  held  in  a  glass  funnel,  and  over  it  pour 
a  warm  solution  of  hyposulphite  of  soda  (six 
or  eight  ounces  in  a  quart  of  water),  which 
rapidly  dissolves  the  chloride  of  silver  from 
the  ore.  Continue  this  treatment  until  a 
small  portion  of  the  filtered  liquid  contained 
in  a  test-tube,  darkens  but  slightly  and  does 
not  lose  its  transparency  upon  the  addition  of 
a  few  drops  of  a  solution  in  water  of  sulphide 
of  sodium. 

Wash  the  mass  in  the  filter  with  warm 
water,  remove  filter  and  all,  dry  and  burn  in 
scorifier  in  muffle,  at  a  low  heat,  mix  ashes 
with  lead,  scorify  and  cupel  as  usual. 

(The  hyposulphite  solution  dissolves  out 
sulphate  of  silver  as  well  as  the  chloride.  If, 
as  is  sometimes  the  case,  it  is  desired  to  know 


APPENDIX.  369 


the  amount  of  sulphate  present,  leach  a  third 
charge  with  warm  water,  which  will  take  out 
the  sulphate,  but  will  not  touch  the  chloride 
or  any  unacted-upon  ore.  Scorify  and  cupel 
the  residue  as  directed.) 

The  difference  between  the  two  cupellations 
shows  the  amount  of  silver  which  has  been 
changed  into  the  state  of  a  chloride.  Thus  : 

ist  charge  ran  180  oz.  per  ton. 
2d  charge  ran  10  oz.  per  ton. 
Hence,  180—10^170  oz.  of  chloridized  pulp. 
To  obtain  percentage  : 

180  :  170  ::  100  :  x  =  94.4  per  cent. 

"  If  there  should  be  gold  in  the  ore,  this 
must  be  subtracted  from  both  assays,  because, 
although  the  amount  of  gold  would  be  equal, 
the  chlorination  result,  as  it  should  be,  must 
come  out  higher  after  the  gold  is  subtracted." 
(Kustel.) 

VIII. —  THE  ASSAY  OF  GOLD  AND  SILVER  BULLION. 

The  larger  portion  of  this  article  is  taken 
from  the  Fourth  Annual  Report  of  the  State 


370  MANUAL    OF  ASSAYING. 

Mineralogist  of  California  for  the  year  ending 
May  15,  1884,  by  the  kind  permission  of  Mr. 
Henry  G.  Hanks,  State  Mineralogist.  His 
very  able  and  complete  paper  could  hardly  be 
improved,  hence  the  extracts  are  given  almost 
verbatim,  as  many  will  not  succeed  in  obtain- 
ing copies  of  the  report,  the  edition  of  which 
is  already  exhausted. 

The  remainder  of  the  description  is  made 
up  partially  from  information  given  me  per- 
sonally by  Mr.  F.  E.  Fielding,  assayer  of  the 
Consolidated  Virginian  and  Consolidated  Cal- 
ifornia Mines,  of  the  Comstock  Lode,  Virginia 
City,  Nevada,  and  partially  from  other  sources, 
together  with  a  little  as  the  results  of  personal 
experience. 

Bullion,  or  the  precious  metals  in  bars  more 
or  less  impure,  is  of  very  varying  composition, 
running  down  from  that  which  is  mostly  gold, 
through  mixtures  where  the  gold  and  silver 
are  more  equally  divided,  and  where  the  silver 
predominates  (all  containing  various  impuri- 
ties or  base  metals,  as  lead,  copper,  etc.),  to 


A  PPENDIX.  371 


base  bullion,  or  that  in  which  the  lead  is  in 
excess  of  all  the  others.  The  latter  kind  is 
treated  of  in  another  portion  of  the  appendix. 
Here  I  consider  only  those  bullions  in  which 
the  gold  and  silver  form  the  greater  amount. 

Absolutely  accurate  assays  of  gold  and  sil- 
ver bullion  require  care,  skill,  and  first-class 
apparatus.  The  skill  may  soon  be  acquired 
by  practice,  but  the  apparatus  must  not  only 
be  of  the  very  best  quality,  but  must  be  kept 
in  the  most  perfect  state  of  adjustment.  It 
is  not  enough  to  purchase  chemicals  which 
are  marked  "  pure,"  or  a  balance  supposed  to 
be  accurate.  The  chemicals  must  be  tested, 
and  the  accuracy  and  adjustment  of  the  bal- 
ance and  weights  verified,  before  correct  re- 
sults can  be  certain. 

The  process  of  assaying  gold  and  silver 
bullion  is  divided  into  several  operations,  as 
follows  :  Melting  and  refining  the  crude  bull- 
ion, and  casting  the  bar,  cutting  the  assay 
chips,  or  otherwise  preparing  the  assay  sam- 
ples, the  preliminary  assay,  the  assay  proper, 


372  MANUAL    OF  ASSAYING. 


calculating  the  results,  weighing  the  bar,  and 
stamping  the  fineness  and  value  upon  it. 

Melting,  refining,  and  casting  the  crude  biill- 
ion. —  For  melting,  a  wind  furnace  is  best,  but 
a  good  coal  stove,  such  as  used  in  offices,  will 
answer  the  purpose  if  the  amount  operated 
upon  is  small. 

The  wind  furnace  is  a  square  box  of  fire- 
bricks, built  in  the  form  of  a  cube  of  three- 
foot  face,  with  an  opening  in  the  centre  of  the 
upper  face.  The  fire-box  is  about  a  foot 
square,  and  fourteen  inches  deep,  provided 
with  an  ash  pit,  movable  grate,  bars,  and  slid- 
ing cast-iron  cover.  The  flue  should  be  a 
horizontal  opening,  about  three  by  six  inches, 
near  the  top  of  the  fire-box,  and  connected 
with  a  chimney  at  least  thirty  feet  high,  to 
insure  a  good  draft.  The  furnace  can  be 
built  by  any  bricklayer  of  ordinary  skill  and 
judgment.  No  mortar  should  be  used  in  lay- 
ing the  fire-brick,  but  good  clay,  mixed  with 
a  portion  of  coarse  sand,  substituted. 

The  bullion   is  generally  melted  in  a  black 


APPENDIX.  373 


lead  crucible.  Before  such  a  crucible  can  be 
safely  used,  it  must  be  annealed.  Were  this 
neglected,  and  it  should  be  placed  in  the  fire 
without  this  precaution,  it  would  soon  fly  to 
pieces.  This  is  caused  by  the  water  it  con- 
tains being  converted  into  steam  ;  and  the 
structure  of  the  material  being  such  that  the 
steam  cannot  make  its  escape,  destruction  of 
the  crucible  follows.  It  is  best  to  commence 
annealing  the  crucible  some  time  before  it  is 
wanted.  It  should  be  set  near  the  hot  fur- 
nace for  several  days,  and  turned  occasionally. 
When  the  fire  is  nearly  spent,  it  may  be 
placed,  rim  downward,  upon  the  hot  sand, 
generally  placed  on  top  of  the  furnace.  A 
day  or  two  of  such  treatment  will  make  it 
safe  to  hold  it  over  the  open  furnace  by  the 
aid  of  the  crucible  tongs  or  poker.  After  it 
has  been  frequently  turned,  and  is  hotter  than 
boiling  water,  it  is  safe  to  place  it,  rim  down- 
ward, upon  the  burning  coals.  After  the  rim 
is  red  hot,  all  danger  is  passedj  and  it  may  be 


374  MANUAL   OF  ASSAYING. 

turned,  and  placed  in  position  for  the  recep- 
tion of  the  gold. 

If  the  fuel  is  charcoal,  it  will  be  best  not  to 
use  small  pieces,  or,  at  least,  not  coal  dust. 
Pieces  the  size  of  an  egg,  or  larger,  will  make 
the  best  fire.  When  the  crucible  becomes 
red  hot,  a  long  piece  of  quarter-inch  gas  pipe 
is  used  to  blow  out  any  dust  or  ashes  that 
may  have  fallen  into  it.  A  cover  is  then 
placed  on  the  crucible,  and  lumps  of  coal  built 
up  around  it  with  a  long  pair  of  cupel  tongs. 
When  the  crucible  has  attained  a  full,  red 
heat,  one  or  two  spoonfuls  of  borax,  wrapped 
in  paper,  are  placed  in  it,  using  the  cupel 
tongs.  When  the  borax  has  melted,  a  small 
quantity  of  the  bullion,  also  wrapped  in  paper, 
is  placed  in  the  crucible  in  the  same  manner. 
Several  portions  may  be  thus  added,  accord- 
ing to  the  size  of  the  crucible.  A  fresh  sup- 
ply of  charcoal  must  be  built  up  around  the 
crucible  when  required,  the  cover  having  been 
previously  replaced.  When  the  bullion  has 
melted  down,  more  is  added  in  the  same  man- 


APPENDIX.  375 


ner,  until  the  crucible  has  received  all  that  is 
to  constitute  the  bar.  In  the  meantime,  the 
ingot  mould,  in  which  it  is  intended  to  cast 
the  gold,  must  be  made  smooth  and  clean 
inside.  This  is  best  done  by  rubbing  with 
sandpaper  and  oil,  or  with  a  dry  piece  of 
pumice  stone.  It  is  then  wiped  dry  and  clean 
with  a  rag,  oiled  slightly,  and  placed  on  the 
edge  of  the  furnace  in  such  a  position  that 
it  may  become  quite  hot ;  not  so  hot,  how- 
ever, as  to  approach  redness,  nor  to  cause  the 
oil  to  burn. 

When  the  bullion  is  in  a  fluid  state  in  the 
crucible,  the  mould  must  be  placed  on  a  level 
surface,  and  oil  poured  into  it.  To  make  a 
clean  bar,  it  will  be  found  best  to  use  consid- 
erable oil  —  sufficient  to  cover  the  bottom  of 
the  mould  to  the  depth  of  at  least  one-fourth 
of  an  inch.  The  mould  should  be  turned  in 
such  a  manner  as  to  allow  the  oil  to  flow  to 
all  parts  of  its  interior,  and  then  placed  again 
level,  and  in  the  position  it  is  to  occupy  while 
casting  the  bullion.  If  the  latter  is  clean, 


376  MANUAL   OF  ASSAYING. 

and  the  quantity  less  than  fifty  ounces,  it  is 
best  not  to  attempt  to  skim  it.  Two  spoon- 
fuls of  nitrate  of  potash  may  be  added,  and 
one  of  carbonate  of  soda,  and  the  whole 
allowed  to  melt  and  flow  over  the  surface  of 
the  melted  metal.  When  very  hot,  and  the 
slag  perfectly  fluid,  the  crucible  is  lifted  from 
the  furnace,  and  with  a  bold  and  steady  hand, 
its  contents  are  poured  into  the  mould,  the 
crucible  being  held  for  a  little  time  in  an 
inverted  position,  to  allow  the  last  portion  of 
metal  to  flow  from  it.  The  oil  inflames,  and 
remains  burning  on  the  slag,  which  flows 
evenly  on  the  surface  of  the  bullion.  If  the 
mould  is  clean,  and  of  the  right  temperature, 
and  if  sufficient  oil  is  used,  a  clean  bar  will 
result.  A  little  practice  will  enable  the  ope- 
rator to  hit  the  exact  conditions.  The  oil 
used  should  be  a  cheap  animal  oil  ;  common 
whale  oil  answers  every  purpose  ;  lard  oil  is 
also  well  suited  ;  coal  oil  is  too  inflammable, 
as  well  as  dangerous,  and  should  never  be 
used.  When  cold,  the  bar  falls  easily  from 


APPENDIX.  377 


the  mould.  A  slight  tap  with  a  hammer  sepa- 
rates the  slag,  and  the  bar  may  be  cleaned 
with  water  and  nitric  acid,  or,  if  necessary, 
with  sand  and  a  suitable  brush.  A  good  plan 
is  to  place  the  bar  in  the  furnace  until  it 
becomes  nearly  red  hot,  and  then  to  quench 
it  suddenly  in  water.  This  will  be  unneces- 
sary if  proper  precautions  have  been  observed 
in  preparing  the  mould. 

When  the  bullion  is  very  impure  —  which 
is  the  case  when  in  the  form  of  retorted  amal- 
gam which  has  not  been  properly  cleaned  — 
a  different  method  of  treatment  should  be 
adopted.  -  A  large-sized  crucible  will  be  re- 
quired. Three  or  four  times  the  amount  of 
flux  must  be  put  in,  with  the  addition  of  a 
spoonful  of  carbonate  of  potash.  A  skimmer  - 
must  be  prepared  by  forming  the  end  of  a 
large  wire,  about  the  size  of  a  common  lead 
pencil,  into  a  spiral  about  an  inch  and  a  half 
in  diameter,  and  bending  it  so  that  when  the 
skimmer  is  let  down  vertically*  into  the  cruci- 
ble the  spiral  will  lie  flat  upon  the  surface  of 


378  MANUAL    OF   ASSAYING. 


its  contents.  A  bucket  of  water  is  set  near 
the  furnace,  and  when  the  slag  has  become 
fluid,  and  it  is  beyond  question  that  the  bull- 
ion has  become  perfectly  melted,  the  skimmer 
is  touched  to  the  slag  and  gently  moved  from 
side  to  side  ;  a  portion  of  the  slag  adheres  to 
the  iron,  the  skimmer  is  removed  and  plunged 
into  the  water,  and  immediately  replaced  in 
the  crucible  ;  an  additional  portion  attaches 
itself  to  the  skimmer,  which  is  again  quenched 
in  water.  This  is  repeated  until  a  large  por- 
tion of  the  slag  is  removed,  and  a  new  charge 
of  flux,  consisting,  this  time,  of  borax  and 
nitrate  of  potash,  is  allowed  to  fuse  upon  the 
surface  of  the  bullion.  The  first  flux  is  re- 
moved from  the  skimmer  by  a  slight  blow 
with  a  hammer,  and  the  crucible  is  skimmed 
with  it  as  before.  This  must  be  repeated 
until  all  iron  and  other  impurities  have  been 
removed,  and  the  surface  of  the  molten  metal 
appears,  when  exposed,  clean  and  reflective 
as  a  mirror.  It  may  then  be  poured  into  the 
mould,  as  described  before.  Care  should  be 


APPENDIX,  379 


taken  not  to  clip  the  wet  skimmer  beneath  the 
surface  of  the  bullion,  or  an  explosion  will 
take  place. 

In  large  meltings  it  is  customary  always  to 
skim  the  bullion  before  pouring,  and  so  far  to 
remove  the  slag  that  any  remaining  portion 
may  be  left  on  the  sides  of  the  crucible,  and 
the  metal  only  allowed  to  flow  into  the  mould. 
This  requires  some  skill  and  considerable 
practice.  As  it  is  imperative  that  the  bar 
should  be  homogeneous  to  insure  a  correct 
assay,  it  is  usual  to  mix  the  melted  metals 
thoroughly  before  pouring.  This  is  done  in 
the  large  way  by  stirring  just  before  lifting 
from  the  furnace.  It  may  be  done  with  an 
iron  rod,  with  a  piece  of  black  lead  held  with 
the  tongs,  or  with  a  clay  stirrer  made  specially 
for  that  purpose,  in  which  case  it  will  be  nec- 
essary to  allow  it  to  remain  in  the  crucible 
until  it  has  acquired  the  temperature  of  the 
fused  metal  ;  otherwise,  a  portion  of  the  bull- 
ion may  attach  itself  to  the  stirrer,  and  be  re- 
moved with  it.  In  small  meltings  it  will  be 


380  MANUAL    OF  ASS  A  YING. 


found  sufficient  to  mix  the  bullion  by  giving 
the  crucible  a  rotary  motion  while  holding  it 
with  the  tongs  just  previous  to  pouring.  This 
must  be  done  so  quickly  that  the  crucible  has 
no  time  to  cool.  For  very  small  fusions  it  is 
best  to  use  a  small  Hessian  crucible,  and, 
when  the  bullion  is  melted  with  plenty  of  flux, 
to  set  it  aside  to  cool,  and  then  break  the  cru- 
cible, and  separate  the  pieces  of  crucible  and 
portions  of  slag  by  slight  blows  of  a  hammer 
on  the  edges  of  the  button.  It  is  very  diffi- 
cult to  pour  small  quantities  of  gold  without 
loss  from  portions  remaining  on  the  sides  of 
the  crucible. 

Preparation  of  samples  for  assay. —  When 
the  bar  is  clean,  a  small  portion  must  be 
taken  from  different  parts  for  assay.  This 
is  done  in  several  ways,  very  frequently  by 
cutting  pieces  from  opposite  corners  or  edges 
with  a  cold-chisel  or  hollow  punch,  but  this  is 
extremely  clumsy,  and  in  every  way  inconven- 
ient. If  the  bar  is  brittle,  a  much  larger 
piece  may  break  off  with  the  chip  than  is  re- 


APPENDIX.  381 


quired.  If  the  proper-sized  chip  is  cut  off 
successfully,  it  is  likely  to  fly  away  and  be 
lost.  A  second  way  of  sampling  is  to  bore 
into  the  bar,  top  and  bottom,  with  a  small 
drill.  This  maybe  done v  in  a  lathe  or  by 
means  of  a  ratchet  drill.  The  bar  should 
be  placed  in  a  clean,  copper  pan,  so  that  no 
loss  may  occur  ;  the  surface  borings,  resulting 
from  the  first  revolutions  of  the  drill,  should 
be  rejected.  Those  that  follow,  to  the  extent 
of  a  little  more  than  one  gramme,  are  to  be 
placed  in  a  suitable  vessel,  and  carefully  pre- 
served for  assay,  each  lot  separate.  Before 
cutting  or  boring  the  bar  the  number  of  the 
assay  should  be  stamped  upon  it,  and  the 
same  number  placed  with  the  clippings  or 
borings.  This  number  should  represent  the 
bar  through  every  stage  of  the  assay  by  which 
its  value  is  ascertained.  Some  assayers  stamp 
the  initial  of  their  name  on  the  cut  faces,  so 
that  no  portion  can  be  removed  after  it  leaves 
their  hands.  A  third  manner  of  sampling  is 
that  by  "  granulation."  While  the  bullion  is 


382  MANUAL    OF  ASSAYING. 

still  in  the  melted  state  in  the  crucible,  but  is 
already  refined,  it  is  well  stirred,  and  two 
samples  are  scooped  up  with  a  small  ladle, 
one  from  the  bottom  of  the  crucible,  and  the 
other  from  the  top.  Each  ladleful  is  poured, 
slowly  and  carefully,  and  .in  a  narrow  stream, 
into  a  clean  copper  basin  containing  warm 
water,  which  is  rotated  quietly  by  means  of  a 
broom  or  paddle.  Keep  the  resulting  granu- 
lated metal  from  top  and  bottom  of  the  cruci- 
ble apart,  drying  each  lot. 

The  selected  pieces  of  the  granulations,  or 
the  chips  cut  from  the  bars,  are  flattened  on 
the  anvil  and  passed  through  the  rolls  until 
thin  enough  to  be  readily  cut  by  the  snip- 
shears.  (Fig-  85.)  They,  or  the  borings,  if 
borings  are  taken,  are  now  ready  for  weigh- 
ing. 

Weights  and  weighing. — For  the  bullion 
assay  a  special  set  of  weights  known  as 
"gold  weights"  is  used.  As  the  basis  of 
the  bullion  assay  is  1,000  parts,  so  the 
unit  of  the  "gold  weight"  system  is  a  1,000 


APPENDIX.  383 


piece,  from  which  the  weights  range  down 
to  a  YOTOT  piece-  The  actual  weight  of 
each  piece  in  this  system  is  one-half  of 
its  corresponding  piece  in  the  French  or 
metric  system;  thus  the  1,000  piece  weighs 
actually  500  milligrammes,  and  so  on.  Gold 
and  silver  in  bullion  are  always  reported  in 
thousandths;  that  is,  in  parts  of  one  thousand, 
taken,  as  before  stated,  as  the  standard  of  the 
assay ;  hence  the  use  of  the  weights  described. 
By  difference  between  the  fineness  and  the 
1,000,  we  learn  the  number  of  parts  of  the 
base  metal  contained  in  the  bullion.  Thus,  if 
1,000  parts  of  a  bullion,  after  treatment, 
weighs  900  parts,  it  has  a  ''fineness"  of  900, 
or  it  is  900  "fine,"  and  the  base  metal  is  100. 
In  weighing,  always  remember  that  the  rider, 
or  index  needle,  when  marking  tenths  for 
gold,  is  to  be  multiplied  by  two,  as  each  mark 
on  the  beam  or  index  plate  only  represents 
TL-  in  the  metric  system,  while  it  should  be  T2Q- 
for  the  "gold  weight"  system.  Half-tenths 


384  MANUAL    OF  ASS  A  YING. 

are  always  reported  in  the  tables  for  gold,  but 
not  in  those  for  silver. 

As  shown  from  the  preceding,  the  metric 
weights  can  be  employed  if.  the  ''gold 
weights"  are  not  obtainable. 

The  method  of  weighing  is  conducted  as 
follows:  The  assayer  seats  himself  before  the 
balance,  having  the  clippings  or  borings  in  a 
convenient  position  inside  the  case.  A  1,000 
piece  (or  half  a  gramme  weight)  is  placed  in 
the  right-hand  pan  of  the  balance,  and  por- 
tions of  the  clippings  or  borings  in  the  other 
until  nearly  correct,  but  the  bullion  should  be 
in  excess.  The  largest  piece  is  then  removed 
by  the  aid  of  a  pair  of  pincers,  and  a  small 
corner  cut  off  with  the  shears.  This  done 
once  or  twice  will  nearly  balance  the  pans; 
but  by  touching  the  piece  of  bullion  selected 
against  a  clean  file,  still  more  minute  portions 
can  be  removed.  By  careful  manipulation 
nearly 'the  exact  point  will  soon  be  obtained; 
but  with  the  greatest  care,  if  the  balance  is 
delicate,  it  will  be  found  nearly  impossible  to 


APPENDIX.  385 


adjust  the  weight  so  perfectly  that  the  index 
needle  will  not  point  either  one  side  or  the 
other  of  the  zero.  In  such  a  case,  it  will  be 
necessary  to  make  a  memorandum  of  the 
error,  and  mark  it  with  the  number  of  the 
assay,  and  in  weighing  the  cornet,  to  take  the 
same  reading  of  the  index  needle. 

Preliminary  Assay. — It  has  been  found  that 
silver  cannot  be  dissolved  out  of  an  alloy  of 
that  metal  with  gold,  unless  the  proportion  of 
silver  is  at  least  two  and  one-half  times  that 
of  the  gold.  If  a  larger  proportion  is  pres- 
ent, the  gold  is  left  after  the  extraction  of 
the  silver  in  the  form  of  a  powder,  and  can- 
not be  dried  and  weighed  without  danger  of 
mechanical  loss.  If  less,  the  gold  protects 
the  silver,  and  the  action  of  the  acid  ceases, 
while  some  of  the  silver  remains  undissolved. 
An  alloy  of  three  parts  of  silver  to  one  of 
gold  was  formerly  taken,  from  which  the 
terms  quartation  and  inquartation  come;  but 
of  late  years  the  above  proportions  have  been 
found  to  be  best. 


386  MANUAL    OF  ASSAYING. 

In  order,  then,  to  form  such  an  alloy,  the 
assayer  should  know  the  amount  of  silver  in 
the  bullion,  that  he  may  consider  it  in  adding 
silver  to  a  bullion  mostly  gold,  or  gold  to  a 
bullion  nearly  all  silver.  The  following  imag- 
inary and  reversed  bullions  will  illustrate 
this  point  plainly: 

BULLION   NO.   I. 

200  parts  gold  need  80  parts  more  to  make  280  parts. 
700     "     silver  =  2^  times  the  280  parts  gold. 
loo     "     base  metal. 

i , ooo     ' ' 

BULLION    NO.    2. 

700  parts  gold 

200     "     silver  need  1,550  parts  more  to  make  1,750  parts  = 

2$  times  the  700  parts  gold. 
100     "     base  metal. 


1,000 

The  proportions  of  silver  and  gold  in  the 
bullion  in  question  are  ascertained  in  several 
ways.  First,  by  merely  looking  at  the  bullion, 
having  had  previously  such  experience  with 
similar  alloys  that  the  knowledge  becomes 
almost  instinctive.  Secondly,  by  direct  com- 
parison with  slips  of  known  "fineness.*1  Third- 
ly, by  use  of  the  touchstone  and  needles. 


APPENDIX.  387 


(For  the  methods  of  making  and  using  the 
latter,  see  the  article  in  Mr.  Hanks'  Report.) 
Fourthly,  by  a  preliminary  fire  assay.  This 
is  by  far  the  best  way,  and  should  always  be 
done  where  great  accuracy  is  required. 

Take  the  1,000  parts  of  the  bullion  already 
weighed  out,  wrap  in  a  piece  of  pure  sheet 
lead  of  about  2  grammes  (30  grains  or  so)  in 
weight,  cupel  and  weigh  the  resulting  bead. 
If  it  seems  mostly  silver,  roll  it  out,  boil  in 
nitric  acid  of  32°  Beaume  (1.26  sp.  gr.), 
decant,  wash,  dry,  ignite,  and  weigh  the  gold. 
If  the  bead  appears  very  yellow,  add  three  or 
four  times  as  much  pure  silver,  wrap  up  to- 
gether in  sheet  lead,  recupel,  part  as  above, 
and  weigh  the  gold.  The  latter  may  come 
down  as  a  fine  powder,  and  a  slight  loss  occur 
in  washing,  but  the  results  will  be  sufficiently 
accurate  for  the  purpose. 

From  the  data  obtained  above,  it  will  be 
easy  to  make  up  the  proper  alloy  for  the 
regular  assay  and  the  proof  centre,  as  shown 
by  the  following  simple  examples: 


388  MANUAL    OF  ASSA  YING. 

Example  No.  i. 

Suppose   the   1,000   parts   of  bullion   taken 
weigh,    after   cupellation,    520.5     parts,    then 
479.5  parts  (1,000  —  520.5)  are  base  metal. 
The  gold,  after  parting,  weighs  15  parts. 
These    figures    enable    us    to    prepare    the 
assay  proper  and  the  proof  centre,  as  hereby 
shown: 

Gold  and  silver  bullion  taken 1,000.0  parts. 

"•     "         "      after  cupellation 520-5       " 

Leaving  base  metal 479.5       " 

Gold  and  silver  after  cupellation 520-5  parts. 

"     after  parting 15.0       " 

Silver  in  the  bullion 5°5-5       " 

5°5-5  X  2.5  =      202.2  parts. 

Deduct  gold  already  in  the  bullion 15.0       " 

Leaving  gold  to  add 187.2       " 

Hence: 

Bullion         {       composed  of  Proof  centre. 

take          J    505.5  parts  silver  =  505.5  parts  silver. 
1,000.0  parts   I   479.5       "     base    =  479.5      "     copper. 

I     15.0      "     gold) 
187.2      "       gold  to  add  )  =  202.2      "     gold. 


1,187.2      "       total.  1,187.2      "     total. 


APPENDIX.  389 


Example  No.  2. 

Gold  and  silver  bullion  taken 1,000.0  parts. 

"      after  cupellation 764.4       " 

Leaving  base  metal 235.6       " 

Gold  and  silver  after  cupellation 764.4  parts. 

"     after  parting 602.  i       " 


Silver  in  the  bullion 162.3       " 

602.1  X  2.5  =  1,505.2  parts. 
Deduct  silver  already  in  the  bullion  ....      162.3       " 


Leaving  silver  to  add 1,342.9       " 

Hence: 

Bullion       f      composed  of  Proof  centre. 

take         ;   602.1  parts  gold      ==    602.1  parts  gold. 
1,000.0  pts.   |    235.6      "      base      =    235.6     "     copper. 

I  162.3      "      silver  ( 
1,342.9     "     silver  to  add  )==i>5o5.2     "     silver. 


2,342.9     "     total.  2,342.9     "     total. 

The  silver,  gold,  and  copper  added  are,  of 
course,  pure. 

The  Assay  Proper. —  Two  assays  of  a  large 
bar  are  always  made,  the  samples  being 
taken  from  the  top  and  bottom.  A  proof 


3QO  MANUAL   OF  ASSAYING. 


centre  or  "check"  is  always  run  through  with 
each  set  of  assays,  and  consists  of  pure  gold, 
pure  silver,  and  pure  copper  in  such  propor- 
tions as  shall  correspond  as  nearly  as  possi- 
ble to  those  of  the  bullion  under  trial,  as 
shown  in  the  above  examples. 

The  proof  cupel  is  always  placed  in  the 
centre  of  the  muffle,  those  for  the  bullions  at 
each  side,  the  object  being  to  correct  the  loss 
by  volatilization. 

The  loss  in  weight  of  the  proof  centre  bead 
is  to  be  added  to  each  weight  of  the  bullion 
bead. 

Make  the  weighings  of  the  duplicate  bul- 
lions, and  the  gold  or  silver  that  is  to  go 
with  each,  and  also  the  three  metals  or  so  for 
the  proof  centre.  Wrap  each  lot  in  a  piece  of 
pure  sheet  lead,  and  squeeze  all  into  a  bullet. 

According  to  the  difference  in  fineness  of 
the  bullions  are  the  amounts  of  pure  sheet 
lead  varied,  and  the  latter  must  contain  no 
gold  whatever.  Its  purity  being  established, 
it  is  easily  prepared  by  rolling  out  to  a  uniform 


APPENDIX.  391 


thickness  (about  -^  inch  or  so),  ancl  about  if 
inches  wide.  The  weight  of  so  many  inches 
of  the  lead  is  determined,  and  the  rest  of  the 
samples  are  cut  from  measurement  of  the  one 
weighed.  These  pieces  are  known  as  "lead 
cornucopias,"  and  should  always  be  prepared 
by  the  assayer  himself,  and  kept  on  hand  in 
sufficient  quantity. 

If  too  much  lead  is  used  in  the  cupellation 
of  the  buttons,  the  loss  in  precious  metals  is 
increased  by  the  greater  length  of  time  re- 
quired for  the  cupellation.  On  the  other 
hand,  if  there  is  a  deficiency  in  lead,  the  beads 
are  ill-shaped,  and  are  liable  to  contain  some 
of  the  base  metals.  If  a  large  amount  of  cop- 
per is  in  the  bullion,  the  lead  must  be  in- 
creased. "Long  experience  has  proved  that 
silver  opposes  the  oxidation  of  copper  by  its 
affinity,  so  that  it  is  necessary  to  add  a  larger 
amount  of  lead  in  proportion  to  the  quantity 
of  silver  present."  (Mitchell.) 

In  cupelling  bullion  say  from  980  to  1,000 
fine,  30  grains  (about  2  grammes)  of  lead  are 


3Q2  MA  NUAL    OF  A  SSA  YING. 

best  used,  and  for  very  base  bullion,  and 
where  the  base  is  mostly  copper,  100  to  130 
grains  (6.5  to  8.5  grammes,  nearly)  are  gener- 
ally used.  Mark  appropriately  with  ruddle 
three  good  cupels,  place  them  in  the  muffle, 
the  proof  cupel  between  the  other  two,  as 
directed  before,  and  when  hot,  a  piece  of  pure 
lead,  weighing  3  grammes  (about  45  grains), 
is  placed  in  each.  The  leads  will  soon  melt 
and  begin  to  "drive";  that  is,  begin  to  be 
absorbed  by  the  cupel ;  the  assays  are  then  to 
be  added,  using  the  cupel  tongs.  When 
perfectly  melted,  the  cupels  are  drawn  forward 
to  that  point  in  the  muffle  which  experience 
has  shown  to  the  assayer  that  cupellation 
progresses  most  successfully.  When  the 
cupellation  is  finished,  and  the  buttons  have 
assumed  a  brilliant  metallic  lustre,  they  are 
removed,  hammered  slightly  on  their  edges 
on  a  clean  anvil,  the  last  blow  being  given 
near  one  edge,  to  make  that  part  thinner,  in 
order  to  facilitate  the  rolling  process  which 
follows,  and  examined  with  a  magnifying  glass 


APPENDIX.  393 


to  see  that  all  bone  ash  has  been  removed. 
Weigh  and  note  results.  The  two  bullion 
beads  should  weigh  exactly  alike;  if  this 
should  not  be  the  case,  the  heavier  one  must 
be  examined  carefully,  to  see  if  any  particle 
of  bone  ash  may  have  been  overlooked.  If 
this  should  fail,  there  is  no  recourse  but  to 
make  another  assay,  which  should  agree  with 
one  of  the  first.  Generally,  if  care  is  used, 
the  first  pair  will  agree.  Then  add  to  the 
weight  of  the  assay  beads  proper  the  loss  sus- 
tained by  the  bead  of  the  proof  centre.  Next 
the  beads  should  be  annealed;  which  can  be 
done  in  the  muffle,  if  still  hot,  or  upon  char- 
coal, with  the  flame  of  a  spirit  lamp  urged 
with  a  blowpipe.  After  cooling,  they  are 
passed  through  the  rolls,  being  drawn  into 
ribbons  about  2\  inches  in  length.  The  proper 
letter  or  number  is  stamped  on  the  end  of 
each  slip,  somewhat  deeply,  and  all  are  then 
re-annealed.  Each  slip  is  then  rolled  up  into 
a  spiral  form  upon  a  glass  rod  or  lead  pencil, 
commencing  at  that  end  of  the  slip  which  is 


394  MANUAL    OF  ASSAYING. 

not  stamped.  A  slight  pinch,  or  reverse  bend, 
after  the  rod  is  removed,  will  prevent  their 
unrolling.  The  "cornets,"  so  prepared,  are 
then  ready  for  treatment  with  acid,  after 
which  step  the  letters  or  numbers  stamped 
upon  them  will  be  as  distinctly  seen  as  they 
were  before. 

Introduce  each  cornet  into  a  separate  part- 
ing flask  or  matrass,  and  add  i  fluid  ounce 
(29^  c.c.)  of  pure  nitric  acid  of  21°  Beaume 
(sp.  gr.  1.16),  place  on  the  sand  bath  which 
acts  as  cover  of  the  furnace,  or  on  a  small 
sand  bath  supported  on  the  ring  of  a  retort 
stand  over  a  spirit  lamp  or  gas  burner,  and 
boil  until  no  more  red  fumes  are  evolved  (say 
ten  minutes).  Just  at  the  point  of  coming  to 
a  boil  add  one  or  two  "pepper  carbons" 
(made  by  heating  whole  or  unground  pepper 
beans  to  carbonization  on  an  iron  shovel  or 
pan).  They  prevent  spirting  or  bumping. 

A  folded  piece  of  paper,  or  a  pair  of  wood- 
en tongs,  is  used  to  lift  the  flasks,  and  the 
acid,  decanted  carefully  into  some  convenient 


APPENDIX.  395 


vessel  kept  to  receive  it,  as  the  silver  is  valu- 
able, and  may  be  recovered  when  a  sufficient 
quantity  has  accumulated.  The  same  quan- 
tity of  32°  Beaume  acid  (1.26  sp.  gr.)  is  then 
poured  into  each  flask,  and,  being  placed  on 
the  sand  bath,  again  boiled  for  ten  minutes, 
with  the  "  pepper  carbons  "-as  usual.  After 
this,  the  acid  is  poured  off,  and  each  flask  is 
filled  up  with  distilled  water,  gently  rotated, 
and  the  water  decanted  and  thrown  away. 
Repeat  the  washing,  and  finally  fill,  for  the 
third  time,  the  flasks  with  distilled  water,  this 
time  quite  to  the  brim.  Over  the  mouth  of 
each  flask  an  annealing  cup  is  placed,  mouth 
downward,  like  a  cap,  and  the  flask  and  cup 
inverted  together.  By  these  means  the  cornet 
is  deposited  gently,  and  without  loss  or  injury 
in  the  cup.  The  flask  is  then  gently  raised 
until  on  a  level  with  the  edge  of  the  cup,  when 
with  a  quick  side  motion  the  flask  is  removed, 
the  water  from  it,  of  course,  running  to  waste. 
The  water  in  the  cup  is  poured  out  carefully, 
and  the  cup  and  its  cornet  are  heated,  at  first 


396  MANUAL    OF  ASSAYING. 

gently  on  the  sand  bath  till  all  the  moisture 
has  been  driven  off,  then  in  the  muffle  to  red- 
ness, making  the  third  time  of  annealing. 
Take  out  and  let  cool.  The  gold  has  recov- 
ered its  natural  color,  and  is  firm  enough  to 
be  handled  with  pincers.  It  must  next  be 
weighed  accurately,  using  the  "gold  weights" 
(or  the  gramme  weights  and  multiplying  by 
two),  and  noting  any  memorandum  regarding 
the  position  of  the  index  in  weighing  out  the 
bullion  in  the  first  operation.  The  weight  of 
the  cornet  in  parts  of  the  1,000  piece  (or  in 
half  milligrammes)  will  represent  the  fineness 
of  gold  in  the  bar,  expressed,  as  before,  in 
thousandths. 

A  small  amount  of  silver  will  always  remain 
in  the  cornet,  no  matter  how  carefully  the 
manipulations  may  have  been  conducted. 
This  surcharge,  so  called,  must  be  deducted 
from  the  weight  of  the  gold  by  subtracting 
from  it  one-half,  one,  or  two  thousandths  (or 
"points")  accordingly  as  the  fineness  ranges 
from  500  to  900,  or  as  experience  indicates. 


APPENDIX.  397 


Weighing  the  Bar.— The  next  step  is  to 
ascertain  the  weight  of  the  bar  in  troy  ounces 
and  decimals.  This  must  be  done  with  the 
greatest  accuracy.  A  good  bullion  balance  is 
much  to  be  desired;  but  a  bar  can  be  weighed 
on  a  defective  balance  if  it  is  sufficiently  deli- 
cate to  turn  distinctly  with  the  hundredth 
part  of  a  troy  ounce.  This  method  of  weigh- 
ing is  called  counterpoising,  and  is  conducted 
as  follows: 

The  beam  must  first  be  brought  to  a  level 
by  putting  sand,  small  shot,  or  other  conven- 
ient weights  into  the  lighter  pan.  When  in 
perfect  equilibrium,  a  small  weight  is  placed 
in  one  of  the  pans  to  test  the  delicacy  of  the 
movement,  and  if  satisfactory,  the  bar  is  laid 
in  one  pan,  and  the  equilibrium  restored  by 
putting  any  convenient  substance,  as  sand, 
into  the  other.  The  bar  is  then  removed, 
and  ounce  weights  put  in  its  place,  which  will 
be  the  exact  weight  of  the  bar,  all  errors  of 
the  apparatus  being  corrected  by  counter- 
poising, which  will  be  evident  to  the  reader 


398  MANUAL   OF  ASSAYING. 

without  further  explanation.  Of  course  the 
ounce  weights  must  be  proved  by  experiment 
to  be  correct  among  themselves. 

It  is  sometimes  impossible  to  obtain  troy 
ounce  weights,  in  which  case  avoirdupois  may 
be  used.  The  same  rule  as  to  accuracy  applies 
equally  to  them.  Each  pound  equals  14.5833 
troy  ounces.  An  excess  of  even  pounds  must 
be  made  with  ounces  and  decimals,  which  can 
be  prepared  by  any  person  of  moderate  me- 
chanical skill.  The  value  of  an  avoirdupois 
ounce  is  0.91 1458  ounce  troy,  or  one-sixteenth 
of  a  pound.  To  make  the  calculation,  it  is 
only  necessary  to  multiply  pounds  by  the 
former  and  ounces  by  the  latter  factor,  and 
add  the  two  together.  The  following  table 
may  be  used  to  facilitate  the  calculation : 


APPENDIX. 

399 

Avoirdupois, 

Troy  Ounces. 

Avoirdupois. 

Troy  Ounces. 

i  ounce 

=        0.911458 

13  ounces 

=       11.848958 

2  ounces 

—         1.822916 

14 

=       12.760416 

3         " 

=         2.734374 

i5         " 

=       13-671874 

4 

=         3-645833 

i   pound 

=       14.583333 

5 

=         4-55729I 

2  pounds 

=       29.166666 

6 

=         5-468749 

3         " 

=     43-749999 

7         " 

=         6.380208 

4 

=     58.333333 

8 

=         7.291666 

5         " 

=     72.916666 

9         " 

=         8.203124 

6 

=     87.499999 

10 

=       9-H4583 

7 

=      102  083333 

ii 

=      10.026041 

8 

=     116.666666 

12              " 

=     IO-937499 

9         " 

—     131.249999 

Suppose  the  bar  to  weigh   twelve  pounds 
and  nine  ounces;  set  the  figures  down  thus: 
10.     pounds. 
2.     pounds. 
.9  ounces. 


12.9 

Look  for  10  pounds  in  the  table,  which  will 
be  the  same  as  i  pound  with  the  decimal 
point  moved  one  place  to  the  right,  145.833; 
opposite  2  pounds  will  be  found  29.166;  9 
ounces  will  be  found  to  be  8.203,  which  are  to 
be  added  as  follows: 


4<DO  MANUAL    OF  ASSAYING. 

10.     pounds 145.833 

2.     pounds 29.166 

.9  ounces 8.203 

12.9  weight  of  the  bar.  183.202  troy  ounces. 

When  decimals  of  an  ounce  are  calculated, 
the  values  may  be  taken  from  the  first  column 
of  the  table.  Suppose  the  decimal  to  be  .7, 
or  T7Q-,  move  the  decimal  point  in  the  seventh 
line  one  place  to  the  left,  and  the  result  will 
will  be  .6380208,  which  is  to  be  added  to  the 
sum  of  pounds  and  ounces. 

The  above  method  of  weighing  is  sometimes 
convenient  in  isolated  mining  localities,  where 
no  accurate  bullion  balance  or  large  sets  of 
Troy  weights  can  be  obtained. 

A  table  having  been  given  to  calculate  Troy 
ounces  from  avoirdupois  pounds,  the  follow- 
ing table  has  been  prepared  to  reverse  the 
operation,  and  it  will  in  many  cases  be  found 
convenient: 


APPENDIX. 


4OI 


Troy 

Ounces . 


TABLE    FOR  CHANGING   TROY   OUNCES    TO    POUNDS    AND 
DECIMALS    AVOIRDUPOIS. 

Troy  Pounds 

Ounces.  Avoirdupois. 

I 06857 

2 I37I4 

3 20571 

4 27428 

5 34285 

Gold  is  always  estimated  in  troy  ounces  and 
decimals.  A  convenient  set  of  weights  may 
be  constructed  as  follows  : 


Pounds 
A  voirdupois. 

6 41142 

7 47999 

8 54856 

9 61713 


Ounces. 
500.  . 
300.. 


Decimals. 
.  o. 500 
.  0.300 


2OO O.  2OO 

100 o.  106 

50 0.050 

20 0.020 


Ounces.  Decimals. 

10 o.oio 

10 o.oio 

5 0.005 

2 O-.002 

2 O.OO2 

I  .  .  .  O.OOI 


Estimation  of  the  Value  of  the  Bar. —  Sup- 
pose the  total  fineness  (silver  and  gold)  to 
be  900,  and  the  fineness  of  gold  as  found 
by  assay  to  be  100;  by  subtracting  the  latter 
from  the  former  the  fineness  will  be  found  to 


4O2  MANUAL    OF  ASSAYING. 

be  800.  Now,  as  one  ounce  of  pure  gold  is 
worth  $20.6718,  one  one-thousandth  will  be 
worth  $0.0206718;  therefore,  an  ounce  of 
alloy,  containing  100  parts  of  pure  gold,  would 
be  worth  $0.02060718 x  100,  or  $2.06718.  The 
last  three  decimals  may  be  disregarded,  unless 
the  bar  is  very  large. 

The  value  of  the  silver  is  obtained  in  the 
same  way.  An  ounce  of  pure  silver  is  worth 
$1.2929,  and  one  one- thousandth  equals 
$0.0012929.  This  multiplied  by  the  fineness 
of  silver  as  found,  would  give  the  value  of  the 
silver  in  each  ounce  of  the  bar. 

Multiplication  may  be  avoided,  and  the  cal- 
culations facilitated,  by  the  employment  of  the 
following  table  : 


APPENDIX. 


403 


TABLE   FOR  DETERMINING    THE   VALUE   OF   GOLD   AND 
SILVER    BULLION. 


Fineness. 

Gold. 

Fineness. 

Silver. 

.000^.  .  .  . 

-010335917312 

.000^  .  .  . 

.000646464646 

.001  .... 

.020671834625 

.001  .... 

.001292929292 

.002 

.041343669250 

.002  .... 

.002585858584 

.003  

.062015503875 

.003  

.003878787876 

.004  .... 

.082687338500 

.004 

.005171717168 

.005  .... 

•i°3359r73i25 

.005  .... 

.006464646460 

.006  .... 

.124031007750 

.OO6  .... 

•007757575752 

.007  .... 

.144702842375 

.007  .... 

.009050505044 

.008  

.165374677000 

.008  

.010343434336 

.009  .... 

.  186046511625 

.009  .... 

.011636363628 

The  manner  of  using  this  table  is  the  same 
as  a  similar  one  described  : 

GOLD. 

ioo  same  as  ooi,  decimal  two  places  right  =  $2.06718 
=  value  of  gold  per  ounce. 

SILVER. 

800  same  as  008,  decimal  two  places  right  =  $1.03434 
=  value  of  silver  per  ounce. 

Value  of  gold  per  ounce $2.06718 

"       silver      "  , 1.03434 


Total  value  per  ounce $3. 10152 


404  MANUAL   OF  ASSAYING. 

These  results,  multiplied  by  the  number 
of  ounces  and  decimals  of  an  ounce  the  bar 
weighs,  would  be  its  value  in  dollars  and 
cents.  Suppose  the  bar  weighed  1,540.6 
ounces,  then  - 

$2.06718x1,540.6=        $3,184.69 

1.03434 X  i,54° •$=  1,593-5° 

Total  value  of  the  bar  =          $4,778. 19 

Stamping  the  Bar. — The  assays  being  com- 
pleted, the  bar  weighed,  the  calculations  made, 
and  values  ascertained,  there  remains  only  to 
stamp  the  bar  with  the  proper  steel  dies,  giv- 
ing the  following  data,  which  must  be  im- 
pressed in  the  bar  before  it  can  be  sold  :  Num- 
ber of  the  bar  (which  is  the  number  of  the 
assay  also);  name  of  assayer;  the  total  weight 
of  the  bar,  given  in  Troy  ounces  and  decimals ; 
fineness  of  gold;  fineness  of  silver;  total  value 
of  the  bar  in  dollars  and  cents  ;  date. 

IX.     THE    ASSAY    OF    BASE    BULLION. 

The  uncertainty  in  the  assay  of  base  bullion 
lies,  not  in  the  determination  of  the  amounts 


APPENDIX,  405 


of  gold  and  silver  present,  but  in  the  difficulty 
of  obtaining  an  average  sample. 

This  question  has  given  rise  to  an  amicable 
discussion  in  the  columns  of  the  Engineering 
and  Mining  Journal,  between  various  parties 
interested  (issues  of  May  20,  June  3,  July  i, 
and  September  9,  1882),  eliciting  some  valua- 
ble information,  which  I  purpose  to  reproduce 
herewith. 

A  base  bullion  may  contain  lead,  silver, 
gold,  copper,  arsenic,  antimony,  and  perhaps 
other  metals,  and  sulphur.  When  this  is 
melted  and  cooled,  it  tends  to  form  alloys  of 
varying  degrees  of  fusibility,  which  with  the 
dross  or  scum  (a  mixture  of  oxides,  sulphides, 
etc.)  make  a  pig  or  bar,  from  which  it  is  not 
an  easy  matter  to  select  a  fair  sample  for 
assay. 

In  many  smelting  establishments  the  sur- 
face of  the  melted  bullion  is  skimmed,  and 
the  clear  lead  ladled  into  the  mould,  till  the 
latter  is  filled  to  within  an  inch  of  the  top, 
and  when  it  has  solidified,  the  mould  is  filled 


406  MANUAL   OF  ASSAYING. 

completely.  There  results  then  a  nice-look- 
ing bar,  composed  of  good  lead  above  and 
below,  with  much  dross  in  the  centre.  This 
would  not  matter  so  much  if  an  equal  portion 
of  the  dross  could  be  gotten  at  for  assay;  but 
there's  the  rub.  The  ordinary  way  of  chip- 
ping the  top  and  bottom  of  the  bar  does  no 
good,  since  it  seldom  cuts  deeper  than  \  inch 
below  the  surface.  Even  a  punch  cutting  a 
chip  f  inch  deep  does  not  solve  the  problem, 
for  it  will  not  reach  the  dross  when  cast  in  the 
middle  of  the  bar. 

Mr.  L.  S.  Austin,  in  the  issue  of  Septem- 
ber 9  of  the  journal  quoted,  suggests  a 
method  which  seems  to  meet  the  requirement. 
"  It  consists  in  the  use  of  the  punch  which  I 
have  already  described  [June  3d  issue],  and 
which  takes  a  chip  of  about  ^  inch  in  diam- 
eter and  uniform  in  thickness.  It  is  driven 
clear  in  to  one-half  the  depth  of  the  bar  by 
the  use  of  a  sledge.  The  bar  being,  say,  four 
inches  in  depth,  a  chip  a  little  over  two  inches 
long  is  then  taken  both  from  top  and  bottom 


APPENDIX,  407 


of  the  bar.  The  chip  is  then  slipped  into  a 
hole  bored  two  inches  deep  into  a  block,  and 
the  projecting  lower  end  trimmed  off  with 
shears  to  the  exact  length  of  two  inches. 
Each  chip  represents,  consequently,  one-half 
the  bar,  its  companion  representing  the  other 
half ;  moreover,  each  chip  is  of  the  same 
weight.  Thus  each  bar  is  represented  accord- 
ing to  its  relative  weight  and  to  its  entire 
depth." 

Having  obtained  these  chips,  they  are  next 
melted,  and  poured  into  a  small  mould.  Take 
this  sample  bar,  cut  slices  across,  each  slice 
being  a  section  of  the  bar.  Cut  from  these 
slices  ^  A.  T.  for  assay.  By  running  five  of 
these  \  A.  T.  assays,  and  uniting  the  silver 
beads  obtained,  for  parting,  the  gold  present 
can  be  accurately  determined. 

Cupel  the  samples,  "feathering"  the  cupels. 
Brittle  or  hard  bullion  can  be  scorified  first,  if 
necessary. 

Consult  the  numbers  of  -the  journal  re- 
ferred to. 


408  MANUAL    OF  ASSAYING. 

X.    QUALITATIVE    TESTS. 

I  have  thought  it  a  good  plan  to  give  a  few 
simple  wet  tests  for  some  of  the  metals,  and 
acids  united  with  them,  as  found  in  ores. 

Ordinarily  these  tests  work  better  on  the 
powdered  ore,  though  sometimes,  as  will  be 
mentioned,  the  original  rock  can  be  directly 
treated. 

Carbonates. — Place  a  drop  of  any  strong 
acid  upon  the  suspected  rock  ;  if  effervescence 
(or  boiling  up)  ensues,  unaccompanied  by 
any  odor,  it  contains  carbonates.  This  test 
does  not  always  show  well  with  small  quanti- 
ties of  carbonates ;  try  then  some  of  the 
powdered  ore  with  acid  in  a  test-tube.  To 
confirm  the  presence  of  carbonic  acid,  suspend 
in  the  test-tube  a  glass  rod  that  has  previously 
been  dipped  in  lime-water ;  the  drop  on  the 
rod  should  become  turbid  or  milky,  owing  to 
the  formation  of  carbonate  of  lime. 

Place  a  small  sample  of  the  pulverized  ore 
in  a  test-tube,  add  to  it  some  nitric  acid,  a 
little  more  than  will  cover  it,  and  heat  till  the 


APPENDIX.  409 


acid  does  not  seem  to  dissolve  any  more  of 
the  ore  ;  let  cool,  after  which  add  as  much 
pure  water  as  there  is  acid,  and  shake. 

Filter,  in  manner  described  under  "Copper 
Analysis,"  p.  335. 

Sulphates. — To  some  of  the  filtered  acid 
solution  add  solution  of  chloride  of  barium 
(or,  if  lead  be  present,  of  nitrate  of  barium). 
A  white  cloudiness  or  precipitate  (which  does 
not  instantly  form  in  dilute  solutions)  shows 
the  presence  of  sulphates. 

Sulphides. — To  a  piece  of  the  rock,  or  to 
some  of  the  powdered  ore,  add  a  drop  of 
nitric  acid.  If  sulphides  are  present  in  any 
quantity,  a  strong  odor,  similar  to  that  of  rot- 
ten eggs,  will  be  given  off. 

Telhtrides. — Take  a  small  piece  of  the  ore 
and  place  it  on  the  cover  of  a  porcelain  cap- 
sule, and  heat  with  the  inner  flame  of  the 
blow-pipe  for  a  couple  of  minutes.  Now  place 
a  drop  of  concentrated  sulphuric  acid  on  the 
cover,  and  let  it  slide  down  to  the  heated 
fragment.  As  soon  as  it  touches  or  ap- 


4IO  MANUAL    OF  ASSAYING. 

preaches  very  near  the  ore  a  beautiful  carmine 
coloration  forms,  strongly  contrasting  with  the 
white  porcelain.  As  the  latter  cools,  the 
color  fades.  Any  white  crockery,  as  a  piece 
of  a  broken  plate  or  saucer,  will  do  to  use  in 
this  test. 

Copper. — To  a  piece  of  the  rock  on  a  white 
porcelain  surface  add  a  few  drops  of  nitric 
acid  and  stir.  Add  now  an  excess  of  ammo- 
nia water.  If  the  mass  turns  blue,  copper  or 
its  compounds  is  undoubtedly  in  the  ore.  If 
the  latter  contains  much  copper,  a  polished 
knife-blade  dipped  in  an  acid  solution  of  it 
will  receive  a  coating  of  metallic  copper. 

Iron.  —  If,  at  the  same  time  the  solution 
treated  with  ammonia  turns  blue,  or  even  if  it 
does  not  do  so,  there  appears  on  the  porce- 
lain  or  in  the  test-tube,  a  reddish-brown  gelat- 
inous mass,  then  iron  is  present. 

As  further  tests  for  iron,  on  one  part  of  an 
old  plate  put  a  crystal  of  sulphocyanide  of 
potassium  and  on  another  a  lump  of  ferrocya- 
nide  of  potassium  (yellow  prussiate  of  potash); 


APPENDIX.  411 


now  pour  on  each  a  little  of  a  hydrochloric  acid 
solution  of  an  ore  containing  iron  ;  a  blood-red 
coloration  with  the  first-named  re-agent,  and  a 
magnificent  blue  precipitate  with  the  second, 
prove  conclusively  the  presence  of  iron  com- 
pounds. Of  course  these  tests  can  be  shown 
with  the  filtered  solution  in  test-tubes. 

Lead. — Drop  a  little  nitric  acid  upon  a  piece 
of  ore  supposed  to  contain  lead,  then  add  a 
little  water,  and  finally  a  crystal  of  iodide  of 
potassium.  A  bright-yellow  precipitate  will 
form  if  lead  is  present. 

Manganese. — The  best  and  simplest  test  for 
manganese  is  to  fuse  the  substance  with  a 
little  carbonate  of  soda  and  nitrate  of  potash 
on  a  strip  of  platinum  in  a  hot  flame.  The 
manganese  unites  with  the  sodium,  forming 
green  manganate  of  soda.  The  manganese 
may  have  to  be  separated  from  other  matters 
in  a  manner  similar  to  the  method  given  under 
the  crucible  process,  p.  241. 

Silver. —  If  this  metal  is  in  *any  appreciable 
quantity  in  an  ore,  it  will  dissolve  in  nitric 


412  MANUAL   OF  ASSAYING. 

acid  (excepting  the  chloride  ores).  To  the 
acid  solution  add  a  little  hydrochloric  acid, 
solution  of  common  salt,  or  even  a  dry  grain 
or  two  of  the  latter.  A  curdy,  white  precipi- 
tate of  chloride  of  silver  is  thrown  down, 
which  is  not  soluble  in  water  (as  is  chloride 
of  lead,  on  the  contrary),  but  dissolves  easily 
in  ammonia  water.  The  precipitate  turns 
black  on  being  exposed  to  light. 

As  stated  above,  chloride  ores  do  not  dis- 
solve in  nitric  acid  ;  therefore,  when  they  are 
suspected  to  be  present,  put  some  of  the  pow- 
dered ore  into  a  small  bottle,  pour  in  a  small 
quantity  of  very  stong  ammonia  water,  cork 
up  the  bottle,  and  let  it  stand  for  a  few  hours. 
The.n  add,  in  slight  excess,  nitric  acid.  The 
white  precipitate  of  silver  chloride  will  at  once 
come  down  if  there  is  any  in  the  ore. 

The  best  test  for  gold  is  the  fire  assay.  To 
learn  the  colors  and  appearances  of  the  tests 
above  given,  try  them  on  the  following  sub- 
stances : 


APPENDIX.  41 


Carbonates Bi-carbonate  of  Soda. 

Sulphates Sulphuric  Acid. 

Sulphides Copper  or  Iron  Pyrites. 

Tellurides Any  Telluride  Ore. 

Copper Copper  Wire. 

Iron Nail  or  Wire. 

Lead Sheet  Lead  or  Galena. 

Silver Silver  Foil  and  Horn  Silver. 

Manganese Black  Oxide  of  Manganese. 

Consult  the  books  on  qualitative  analysis 
for  further  information  or  tests. 

XI.       BRIEF   SCHEME    FOR   SILICA,  IRON,  AND 
MANGANESE. 

It  is  very  often  the  case  that  the  percent- 
ages in  an  ore  of  the  above-mentioned  sub- 
stances are  wanted.  More  particularly  is  this 
true  with  carbonate  ores.  Hence  the  follow- 
ing notes  : 

Dissolve  the  weighed  ore  in  hydrochloric 
acid  by  the  aid  of  heat.  Filter  hot,  and  wash 
with  hot  water.  The  filtrate  contains  the  iron, 
with  chloride  of  lead,  etc. 

The  silica  on  filter  contains  chloride  of  lead. 


4 1  4  MANUAL  OF  A  SSA  YING. 

Wash  this  out  with  hot  solution  of  citrate  of 
ammonium,  following  with  hot  water.  Ignite 
the  silica  while  still  damp. 

To  the  iron  in  solution  in  the  filtrate  add 
sufficient  sulphuric  acid  to  convert  all  the  lead 
into  sulphate  of  lead.  Warm  the  solution,  if 
not  already  so,  and  add,  drop  by  drop,  dilute 
stannous  chloride  solution,  until  the  liquid  be- 
comes colorless,  showing  that  the  iron  is  all 
reduced  to  state  of  protoxide.  Avoid  a  great 
excess  of  the  tin  solution.  Now  cool,  and  add, 
all  at  once,  an  excess  of  strong  mercuric  chlo- 
ride solution.  The  precipitate  formed  should 
be  perfectly  white.  If  dark-colored,  it  indi- 
cates that  insufficient  mercuric  chloride  has 
been  used,  and  the  analysis  is  spoiled.  If  the 
precipitate  is  all  right,  the  solution  is  ready 
for  titration  with  standard  bi-chromate  of 
potash  solution.  (Consult  Fresenius'  "  Quali- 
tative and  Quantitative  Analysis,"  and  Hart 
and  Sutton  on  "  Volumetric  Analysis.") 

For  manganese  in  ores  (excepting  silicates), 
heat  a  weighed  sample  in  crucible  in  open  fire 


APPENDIX.  415 


for  fifteen  minutes,  converting  the  manganese 
into  protosesquioxide  of  manganese.  Treat 
with  hydrochloric  acid,  and  titrate  with  iodide 
of  potassium  and  hyposulphite  of  sodium. 
(See  Sutton.) 

XII.     DETERMINATION    OF    MOISTURE    IN   AN   ORE. 

It  is  often  a  matter  of  importance  to  know 
the  amount  of  moisture  or  water  contained  in 
an  ore.  The  simplest  manner  in  which  to  de- 
termine this,  and  a  satisfactory  one  at  that,  is 
to  sample  out  a  certain  weight,  say  five 
grammes,  and  transfer  to  a  porcelain  capsule, 
the  weight  of  which  is  already  known.  Ex- 
pose the  capsule  and  contents  to  steam  heat, 
in  any  convenient  way,  for  one-half  hour,  then 
weigh.  Heat  half  an  hour  longer  and  weigh 
again.  There  should  be  but  a  slight  differ- 
ence in  the  last  two  weighings.  The  difference 
between  the  last  weight  and  the  original 
weight  of  dish  and  ore  is  the  loss  by  driving 
off  the  water  ;  this  difference  divided  by  the 
amount  of  ore  taken,  and  multiplied  by  100, 
is  the  percentage  of  moisture  in  the  ore. 


4 1 6  MANUAL    OF  A SSA  YING. 

XIII.      DETERMINATION   OF   SULPHUR  IN  PYRITES. 

Weigh  i  gramme  (or  say  10  grains)  of  the 
finely  powdered  ore  into  a  casserole  ;  add  a 
small  amount  of  chlorate  of  potash,  cover 
with  watch  glass,  add  50  c.c.  concentrated 
nitric  acid,  and  heat  to  boiling,  adding  a  little 
more  chlorate  from  time  to  time.  When  per- 
fectly oxidized,  remove  watch  glass  (and  it 
should  be  rinsed  into  the  casserole),  and  evap- 
orate to  small  bulk  on  a  water  bath.  Add  a 
little  strong  hydrochloric  acid,  and  evaporate 
to  dryness,  moisten  with  the  same  acid,  add 
water  and  filter  from  silica  and  the  gangue. 

To  the  filtrate  add  i  gramme  (or  10  to  15 
grains)  tartaric  acid,  heat,  add  hot  solution  of 
baric  chloride,  drop  by  drop,  boil,  let  settle, 
filter  and  wash  well  with  hot  water. 

Weigh  a  clean  porcelain  or  platinum  cruci- 
ble, add  filter  and  precipitate,  burn  to  ashes, 
cool,  weigh  as  baric  sulphate:  after  deducting 
weights  of  crucible  and  filter  ash,  multiply 
remainder  by  0.1374,  and  the  product  by  100 
or  10  for  percentage  of  sulphur. 


SECTION    II. 


LISTS   AND    REFERENCES. 
GOLD. 

LIST    OF    THE    PRINCIPAL   GOLD    MINERALS   FOUND   IN    THE 
UNITED    STATES. 


NAME. 

1.  Calaverite  (telluride  of  gold). 

2.  Gold  amalgam. 

3.  Electrum  (argentiferous  gold). 

4.  Miillerite    (telluride  of   gold, 
silver  and  lead). 

5.  Nagyagite    (black    tellurium, 
foliated    tellurium,    telluride 
of  gold  and  lead). 

6.  Native  gold  (flour,  leaf,  wire, 
nugget,  free,  etc.).    « 

7.  Petzite  (telluride  of  gold  and 
silver). 

8.  Sylvanite  (graphic  tellurium, 
yellow  tellurium,  telluride  of 
gold  and  silver) 


COMPOSITION. 

Gold,  tellurium. 

Gold,  mercury. 

Gold,  silver. 

Gold,  silver,  lead, 
tellurium. 

Gold,  lead,  tellu- 
rium (antimony, 
sulphur). 

Gold. 

Gold,  silver,  tellu- 
rium. 

Gold,  silver,  tellu- 
'    rium  (antimony). 


41  8  MANUAL   OF  ASSAYING. 

MINERALS    LIKELY    TO    CARRY    GOLD. 

1.  Aikinite.  14.  Magnolite. 

2.  Altaite.  15.  Melaconite. 

3.  Argentite.  16.  Native  arsenic. 

4.  Arsenopyrite.  17.         "       bismuth. 

5.  Bismuthinite.  18.         "       silver. 

6.  Chalcopyrite.  19.         "       tellurium. 

7.  Coloradoite.  20.  Pyrite. 

8.  Ferro-tellurite  21.  Sphalerite. 

9.  Galenite.  22.  Tellurite. 

10.  Henryite.  23.  Tellurpyrite. 

11.  Hessite.  24.  Tetradymite. 

12.  Joseite.  25.  Tetrahedrite. 

13.  Lionite.  26.  Wehrlite. 

SILVER. 

LIST     OF     THE     PRINCIPAL    SILVER     MINERALS     FOUND     IN 

THE    UNITED    STATES. 
NAME.  COMPOSITION. 

1.  Alaskaite   (sulphide    of    bis-      Silver,     bismuth, 
muth,  silver  and  lead).  lead,  copper,  sul- 
phur. 

2.  Argentite  (sulphuret  or  sul-      Silver,  sulphur, 
phide  of  silver,  vitreous  silver, 

silver  glance). 

3.  Bromyrite  (bromide  of  silver,      Silver,  bromine, 
bromic  silver). 


APPENDIX. 


419 


4.  Cerargyrite  (muriate  or  chlo- 
ride of  silver,  horn-silver) 

5.  Dyscrasite    (antimonial    sil- 
ver). 

6.  Electrum  (argentiferous 
gold). 

7.  Embolite  (chloro-bromide  of 
silver). 

8.  Freieslebenite      (antimonial 
sulphide  of  silver  and  lead). 

9.  Hessite   (telluride   of   silver, 
telluric  silver). 

10.  lodyrite    (iodide    of    silver, 
iodic  silver). 

11.  Miargyrite  (sulphide  or  sul- 
phuret  of  silver  and  antimony) 

12.  Native  silver  (free,  wire,  leaf, 
dendritic,  etc.). 

13.  Petzite  (telluride  of  silver  and 
gold). 

14.  Polybasite  (sulphide  of  silver, 
antimony  and  arsenic). 

15.  Proustite(arsenical  silverore, 
light  red  silver  ore,  ruby  sil- 
ver). 


Silver,  chlorine. 
Silver,  antimony. 
Silver,  gold. 

Silver,  chlorine, 
bromine. 

Silver,  lead,  anti- 
mony, sulphur. 

Silver,  tellurium. 

Silver,  iodine. 

Silver,     antimony, 

sulphur. 
Silver. 

Silver,  gold,  tellu- 
rium. 

Silver,  antimony, 
arsenic,  copper, 
sulphur. 

Silver,  arsenic,  sul- 
phur. 


42O 


MANUAL    OF  ASSAYING. 


1 6.  Pyrargyrite  (antimonial  red 
silver  ore,  dark  red  silver  ore, 
ruby  silver). 

17.  Schapbachite      (bismuth-sil- 
ver, sulphide  of  bismuth,  sil- 
ver and  lead). 

1 8.  Schirmerite  (same  as  above 
but  proportions  varying). 

1 9.  Stephanite  (sulphide  of  silver 
and  antimony,  brittle  silver, 
black  silver). 

20.  Sternbergite  (sulphide  of  sil- 
ver and  iron). 

21.  Stetefeldite   (oxide    of   anti- 
mony with  silver,  etc.). 

22.  Stromeyerite  (sulphide  or  sul- 
phuret  of  silver  and  copper, 
silver-copper  glance). 

23.  Sylvanite  (graphic  tellurium, 
yellow  tellurium,  telluride  of 
silver  and  gold). 

24.  Tetrahedrite     (gray    copper 
ore,  sulphide  of  copper,  anti- 
mony, silver,  etc.).     .- 


Silver,  antimony, 
sulphur. 

Silver,  bismuth, 
lead,  sulphur. 

Silver,  bismuth, 
lead,  sulphur. 

Silver,  antimony, 
sulphur. 

Silver,  iron,  sul- 
phur. 

Silver,  antimony, 
copper,  oxygen, 
sulphur. 

Silver,  copper,  sul- 
phur. 

Silver,  gold,  tellu- 
rium (antimony). 

Silver,  copper,  an- 
timony, sulphur 
(arsenic,bismuth, 
mercury,  zinc, 
etc.) 


APPENDIX. 


421 


MINERALS    LIKELY    TO    CARRY    SILVER. 


1.  Algodonite. 

2.  Altaite. 

3.  Arsenopyrite. 

4.  Barnhardite. 

5.  Bornite. 

6.  Boulangerite. 

7.  Calaverite. 

8.  Cerussite. 

9.  Chalcopyrite. 

10.  Coloradoite. 

11.  Enargite. 

12.  Ferro-tellurite. 

13.  Galenite. 

14.  Geocronite. 

15.  Gold  amalgam. 

16.  Henryite. 

17.  Hessite. 

18.  Joseite. 

19.  Leucopyrites. 

20.  Lionite. 

21.  Magnolite. 


22.  Melaconite. 

23.  Miillerite. 

24.  Nagyagite. 

25.  Native  antimony. 
26         "        arsenic. 

27.  "        bismuth. 

28.  "        copper. 

29.  "        gold. 

30.  "        mercury. 

31.  "        tellurium. 

32.  Petzite. 

33.  Pyrite. 

34.  Realgar. 

35.  Smaltite. 

36.  Sphalerite. 

37.  Sylvanite. 

38.  Tellurite. 

39.  Tellurpyrite. 

40.  Tetradymite. 

41.  Wehrlite. 


422 


MANUAL   OF  ASSAYING. 


COPPER. 

LIST    OF    THE     PRINCIPAL     COPPER     MINERALS     FOUND     IN 
THE    UNITED    STATES. 


NAME. 

1.  Aikinite  (needle  ore,  acicular 
bismuth,  cupreous  bismuth). 

2.  Algodonite  (arsenide  of  cop- 
per). 

3.  Atacamite  (muriate  of   cop- 
per, oxy-chloride  of  copper). 

4.  Aurichalcite    (carbonate     of 
zinc  and  copper). 

5.  Azurite  (mountain  blue,  blue 
carbonate     of     copper,    blue 
malachite,  azure  copper  ore). 

6.  Barnhardite  (sulphide  of  iron 
and  copper). 

7.  Bornite  (purple  copper  ore, 
variegated  copper  ore,  erubes- 
cite,   sulphide   of  copper  and 
iron,  horseflesh  ore). 

8.  Bournonite  (triple  sulphuret 
of  copper,  lead  and  antimony). 

9.  Brochantite  (sulphate  of  cop- 
per). 


COMPOSITION. 

Copper,      bismuth, 

lead,  sulphur. 
Copper,  arsenic. 

Copper,  chlorine, 
oxygen  (water). 

Copper,  zinc,  car- 
bon, oxygen 
(water). 

Copper,  carbon, 
oxygen  (water). 

Copper,  iron,  sul- 
phur. 

Copper,  iron,  sul- 
phur. 


Copper,  lead,  anti- 
mony, sulphur. 

Copper,  oxygen, 
sulphur  (water). 


APPENDIX. 


423 


10.  Caledonite     (cupreous     sul- 
phato-carbonate  of  lead). 

11.  Carrollite  (sulphide  of  cobalt 
(nickel)   and  copper). 

12.  Chalcanthite     (blue     vitriol, 
copper     vitriol,     sulphate    of 
copper). 

13.  Chalcocite    (copper    glance, 
vitreous  copper,  sulphuret  or 
sulphide  of  copper). 

14.  Chalcopyrite  (copper  pyrites, 
pyritous  copper,  sulphide  of 
copper  and  iron). 

15.  Chrysocolla(mountain green, 
mountain  blue,  silicate  of  cop- 
per). 

16.  Covellite  (indigo  copper,  blue 
copper,  sulphide  of  copper). 

17.  Cuprite  (red  oxide  of  copper, 
cupreous  oxide,  tile  ore). 

1 8.  Domeykite  (arsenical  copper, 
arsenide  of  copper). 

19.  Enargite    (sulph-arsenite   of 
copper). 

20.  Harrisite(sulphide  of  copper) 


Copper,  lead,  car- 
bon, oxygen,  sul- 
phur. 

Copper,  cobalt 
(nickel),  sulphur. 

Copper,  oxygen, 
sulphur  (water). 

Copper,  sulphur. 


Copper,    iron,    sul- 
phur. 

Copper,  silicon,  ox- 
ygen (water). 

Copper,  sulphur. 
Copper,  oxygen. 
Copper,  arsenic. 

Copper,  arsenic,sul- 

phur. 
Copper,  sulphur. 


424 


MANUAL    OF  ASSAYING. 


21.  Malachite  (mountain  green, 
green    carbonate   of    copper, 
green  malachite, greencopper). 

22.  Melaconite    (black    oxide  of 
copper,  black  copper,  cupric 
oxide). 

23.  Native     copper    (sometimes 
with  silver). 

24.  Pseudomalachite  (phosphate 
of  copper). 

25.  Stromeyerite    (sulphuret    of 
silver  and  copper,  silver-cop- 
per glance). 

26.  Tennantite  (sulph-arsenite  of 
copper). 

27.  Tetrahedrite    (gray    copper 
ore,  sulphide  of  copper  and 
antimony  with  various  other 
sulphides). 

28.  Torbernite    (copper-uranite, 
phosphate   of    uranium    and 
copper). 

29.  Uranochalcite  (oxide  of  uran- 
ium with  oxide  of  copper  and 
sulphate  of  lime) 


Copper,  carbon,  ox- 
ygen (water). 

Copper,  oxygen. 


Copper  (silver). 

Copper,  oxygen, 
phosphorus 
(water). 

Copper,  silver,  sul- 
phur. 

Copper,  arsenic, 
sulphur  (iron). 

Copper,  antimony, 
sulphur  (arsenic, 
bismuth,  silver, 
mercury,  zinc, etc) 

Copper,  uranium, 
phosphorus,  ox- 
ygen (water). 

Copper,  uranium, 
oxygen,  sulphur, 
calcium  (water). 


APPENDIX. 


425 


30.  Vauquelinite    (chromate    of      Copper,  lead,  chro- 
copper  and  lead).  mium,  oxygen. 

31.  Whitneyite  (arsenide  of  cop-      Copper,  arsenic, 
per). 

LEAD. 

LIST    OF    THE    PRINCIPAL    LEAD   MINERALS    FOUND   IN    THE 

UNITED    STATES. 
NAME.  COMPOSITION. 


1.  Alaskaite   (sulphide    of    bis- 
muth, silver  and  lead). 

2.  Altaite  (telluride  of  lead). 

3.  Anglesite    (lead-vitriol,    sul- 
phate of  lead). 

4.  Boulangerite     (sulphide     of 
lead  and  antimony). 

5     Bournonite  (triple  sulphuret 
of  copper,  lead  and  antimony). 

6.  Caledonite  (cup reous-sul- 
phato-carbonate  of  lead). 

7.  Cerussite    (white    lead    ore, 
carbonate  of  lead). 

8.  Dechenite  (vanadate  of  lead 
and  zinc). 

9.  Descloizite      (vanadate      of 
lead). 


Lead,  bismuth,  sil- 
ver, copper,  sul- 
phur. 

Lead,  tellurium. 

Lead,  oxygen,  sul- 
phur. 

Lead,  antimony, 
sulphur. 

Lead,  copper,  anti- 
mony, sulphur. 

Lead,  carbon,  cop- 
per, oxygen,  sul- 
phur. 

Lead,  carbon,  oxy- 
gen. 

Lead,  vanadium, 
zinc,  oxygen. 

Lead,  vanadium, 
oxygen. 


426 


MANUAL   OF  ASSA  YING. 


10.  Freieslebenite      (antimonial 
sulphide  of  silver  and  lead). 

11.  Galenite  (galena,  sulphide  or 
sulphuret  of  lead). 

12.  Geocronite  (sulph-arseno-an- 
timonite  of  lead). 

13.  Henryite  (telluride  of  .lead, 
with  a  little  iron). 

14.  Jamesonite    (sulph-antimon- 
ite  of  lead). 

15.  Kobellite  (sulphide  of  lead, 
bismuth  and  antimony). 

16.  Lanarkite  (sulphato-carbon- 
ate  of  lead). 

17.  Leadhillite  (sulphato-tri-car- 
bonate  of  lead). 

1 8.  Massicot      (plumbic     ochre, 
yellow  oxide  of  lead). 

19.  Mimetite    (green    lead    ore, 
arsenate  of  lead). 

20.  Minium  (red  oxide  of  lead). 

21.  Miillerite  (telluride  of  gold, 
silver  and  lead). 


Lead,    silver,   anti- 
mony, sulphur. 
Lead,  sulphur. 

Lead,  antimony, 
arsenic,  sulphur. 

Lead,  tellurium, 
iron. 

Lead,  antimony, 
sulphur  (iron). 

Lead,  bismuth,  an- 
timony, sulphur. 

Lead,  carbon,  oxy- 
gen, sulphur. 

Lead,  carbon,  oxy- 
gen, sulphur. 

Lead,  i  part;  oxy- 
gen, i  part. 

Lead,  arsenic,  oxy- 
gen (chlorine, 
phosphorus). 

Lead,  3  parts;  oxy- 
gen, 4  parts. 

Lead,  gold,  silver, 
tellurium. 


APPENDIX. 


427 


22.  Nagyagite  (black  tellurium, 
foliated  tellurium,  telluride  of 
gold  and  lead). 

23.  Native  lead. 

24.  Plumbogummite  (phosphate 
of  alumina  and  lead). 

25.  Pyromorphite       (phosphate 
and  chloride  of  lead). 

26.  Schapbachite      (bismuth-sil- 
ver, sulphide  of  bismuth,  sil- 
ver and  lead). 

27.  Schirmerite  (same  as  above 
but  proportions  varying). 

28.  Stolzite  (tungstate  of  lead). 

29.  Vauquelinite    (chromate     of 
copper  and  lead). 

30.  Wulfenite  (yellow  lead   ore, 
yellow   lead-spar,   molybdate 
of  lead). 


Lead,  gold,  tellu- 
rium (antimony, 
sulphur). 

Lead. 

Lead,  aluminum, 
oxygen,  phos- 
phorus. 

Lead,  phosphorus, 
oxygen,  chlorine. 

Lead,  bismuth,  sil- 
ver, sulphur. 

Lead,  bismuth,  sil- 
ver, sulphur. 

Lead,  tungsten,  ox- 
ygen. 

Lead,  copper,  chro- 
mium, oxygen. 

Lead, molybdenum, 
oxygen. 


Note. — For  descriptions  of  the  above,  and  of  other  American 
and  foreign  minerals  of  gold,  silver,  copper  and  lead,  consult 
Dana's  System  of  Mineralogy,  5th  Ed.  with  Sup.,  and  Prof.  J. 
Alden  Smith's  Report  as  State  Geologist  of  Colorado,  for  1880. 


428  MANUAL   OF  ASSAYING. 

LIST    OF    USEFUL    BOOKS    ON    SUBJECTS    MORE    OR    LESS 
CONNECTED    WITH    ASSAYING. 

General  Science. 

Johnson's  New  Universal  Cyclopaedia.  4  vols.  Vols.  i 
and  2,  1876;  vol.  3,  1877;  vol.  4,  1878.  New  York. 

General  Chemistry. 

Watts,  H.  :  A  Dictionary  of  Chemistry.  10  vols.  Vols. 
1-6,  1868;  ist  sup.,  1872;  2d  sup.  (vol.  7),  1875;  3d 
sup.  (vol.  8),  Part  I,  1879;  Part  II,  1881.  London. 

Chemical  Technology. 

Wagner,  R. :  A  Hand-book  of  Chemical  Technology. 
Translated  from  8th  German  edition  by  William 
Crookes.  New  York,  1872. 

Reference  Books  on  Chemistry. 

Roscoe,  H.  E.,  and  C.  Schorlemmer  :  A  Treatise  on  Chem- 
istry. 2  vols.  Vol.  i,  The  Non-Metallic  Elements, 
1878;  vol.  2,  Metals,  Parts  I  and  II,  1879.  New 
York. 

Miller,  W.  A. :  Elements  of  Chemistry,  Theoretical 
and  Practical.  3  vols.  6th  edition.  London, 
1877-1880. 

Text-books  on  Theoretical  Chemistry. 

Barker,  Geo.  F. :  A  Text-book  of  Elementary  Chemis- 
try, Theoretical  and  Inorganic.  Louisville. 


APPENDIX.  429 


Roscoe  H.  E.  :  Lessons  in  Elementary  Chemistry,  In- 
organic and  Organic.  New  edition.  London,  1880. 

General  Qualitative  Analysis. 

Fresenius,  C.  R. :  Manual  of  Qualitative  Chemical  Anal- 
ysis. 9th  English  edition.  London,  1876. 

Douglas,  S.  H.,  and  A.  B.  Prescott :  Qualitative  Chem- 
ical Analysis.  3d  edition.  New  York,  1880. 

Eliot,  C.  W.,  and  F.  H.  Storer :  A  Compendious  Man- 
ual of  Qualitative  Chemical  Analysis.  New  York, 
1879. 

General  Quantitative  Analysis. 

Fresenius,  C.  R.:  Manual  of  Quantitative  Chemical 
Analysis.  7th  English  edition.  London,  1876. 

Classen,  A.:  Elementary  Quantitative  Analysis.  Trans- 
lated by  E.  F.  Smith.  Phila.,  1878. 

Cairns,  F.  A.:  A  Manual  of  Quantitative  Chemical 
Analysis  for  the  Use  of  Students.  New  York, 
1880. 

Special  Quantitative  Analysis. 
Rammelsberg,  C.:    Guide  to  a  Course  of  Quantitative 

Chemical  Analysis,  especially  of  Alloys,  Minerals 

and  Furnace  Products.     Translated  by  J.  Towler. 

New  York,  1872. 
Wohler,  F.:    Hand-book  of  Mineral  Analysis.     Phila., 

1870. 


430  MANUAL    OF  ASSAYING. 

Volumetric  Analysis. 
Sutton,  f.:    A  Systematic   Hand-book   of   Volumetric 

Analysis.     4th  edition.     London,  1882. 
Hart,  Edward :    A  Hand-book  of  Volumetric  Analysis. 

New  York,  1878. 

Laboratory  Manipulation. 

Morfit  (Campbell  and  Clarence] :  Chemical  and  Phar- 
maceutical Manipulations.  Phila.,  1857. 

Williams,  C.  G.:  A  Hand-book  of  Chemical  Manipula- 
tion. London,  1857;  supplement,  1879. 

Geology. 
Cotta,  Bernh.  v.   Treatise  on  Ore  Deposits.     Translated 

from  2d  German  edition  by  F.  Prime,  and  revised 

by  author.     New  York,  1870. 
Dana,  J.  D.:   A  Text-book  of  Geology.      2d   edition. 

New  York,  1874. 

Dana,  J.  D.:    Manual  of  Geology.     New  York,  1881. 
Le  Conte,  Joseph  :    Elements  of  Geology.     A  text-book 

for  colleges  and  for  the  general  reader.    New  York, 

1878. 
Rutley,  C.  L.:   The  Study  of  Rocks.     2d  edition.     New 

York,  1880. 

Mineralogy. 

Dana,  J.  D.:  A  System  of  Mineralogy.  5th  edition, 
1868;  Appendix  I,  1872;  Appendix  II,  1875;  Ap- 
pendix III,  1882.  New  York. 


APPENDIX.  431 


Dana,  J.  D.:    Manual  of    Mineralogy  and    Lithology. 

3d  edition.     New  York,  1878. 
Brush,  G.  J.:   Manual   of    Determinative  Mineralogy, 

with    an    Introduction   on  "  Blow-pipe  Analysis." 

New  York,  1878. 
Foye,  J.  C.:  Tables  for  the  Determination,  Description, 

and  Classification  of  Minerals.     Chicago,  1882. 
Frazer,  P.:  Tables  for  the  Determination  of  Minerals. 

Phila.,  1874. 
Hanks,  H.  G.:    Fourth   Annual    Report   of    the    State 

Mineralogist  of  California.     Sacramento,  1884. 

£  low -pipe  Analysis. 

Plattners  Manual  of  Qualitative  and  Quantitative  Anal- 
ysis with  the  Blow-pipe.  Translated  by  H.  B. 
Cornwall.  4th  edition.  Revised  and  corrected. 
New  York,  1880. 

Cornwall,  H.  B.:  Manual  of  Blow-pipe  Analysis,  Qual- 
itative and  Quantitative.  With  a  Complete  Sys- 
tem of  Determinative  Mineralogy.  New  York,  1882. 

Atwood,  Geo.:  Practical  Blow-pipe  Assaying.  New 
York,  1881. 

Plympton,  G.  W.:  The  Blow-pipe.  A  Guide  to  its  Use 
in  the  Determination  of  Salts  and  Minerals.  New 
York,  1874. 

Elderhorst,  Wm.:  Manual  of  Qualitative  Blow-pipe 
Analysis.  Revised  by  H.  B.  Nason.  Phila.,  1881. 


432  MANUAL    OF  ASSAYING. 

Ross,  W.  A.:  The  Blow-pipe  in  Chemistry,  Mineralogy, 

and  Geology      London,  1884. 
Ross,W.A.:  Pyrology,or  Fire  Chemistry.  London, 1875. 

Metallurgy  and  Mining. 

Kerl,  Prof.:  Practical  Treatise  on  Metallurgy.  Trans- 
lated by  Wm.  Crookes  and  E.  Rohrig.  Vol.  i, 
Lead,  Silver,  Zinc,  etc.,  1868;  Vol.  2,  Copper  and 
Iron,  1869;  Vol.  3,  Steel,  Fuel,  and  Supplement, 
1870.  London. 

Lock,  A.  G.:  Gold;  Its  Occurrence  and  Extraction. 
London  and  New  York,  1882. 

Percy,  John :  Metallurgy.  The  Art  of  Extracting  Met- 
als from  their  Ores.  Part  I,  Silver  and  Gold. 
London,  1880. 

Percy,  John:  The  Metallurgy  of  Lead.    London,  1870. 

Percy,  John :  The  Metallurgy  of  Fuel,  Wood,  Peat, 
Coal,  Charcoal,  Fire-cteys.  Revised  edition. 

Cation,  J.:  Lectures  on  Mining.  3  vols.  London  and 
Paris.  1876-81. 

Lamborn,  R.  H.:  Metallurgy  of  Copper.  6th  edition. 
London,  1875. 

Lamborn,  R.  H.:  Metallurgy  of  Silver  and  Lead.  6th 
edition.  London,  1878. 

Kustel,  G.:  Roasting  of  Gold  and  Silver  Ores,  and  the 
Extraction  of  their  Respective  Metals  without 
Quicksilver.  New  edition  (2d).  San  Francisco, 
1880. 


APPENDIX.  433 


Makin,  G.  H.:  A  Manual  of  Metallurgy.     2d  edition. 

London,  1873. 
Collins,  J.  H.:  A  First  Book  of  Mining  and  Quarrying. 

London,  1872, 
Boivie,  Aug.  J.,  Jr.:  A  Practical  Treatise  on  Hydraulic 

Mining  in  California.     New  York,  1885. 
Davies,  D.  C.:    A   Treatise  on   Metalliferous   Minerals 

and  Mining.     2d  edition.     London,  1881. 
Dames,  D.  C.;  A  Treatise  on  Earthy  and  other  Min- 
erals and  Mining.     London,  1884. 
Egleston,  T.:  Metallurgy  of  Gold,  Silver,  and  Mercury 

in   the  United   States.     London  and   New  York, 

1886. 
Phillips,  J.  A.:  Mining  and  Metallurgy  of  Gold  and 

Silver,     London,  1867. 
Phillips,  J.  A.:  A  Treatise  on  Ore  Deposits.     London. 

1884. 

Phillips,  J.  A.:  Elements  of  Metallurgy.    London,  1874. 
Pomeroy,  H.  R.:  Mining  Manual  for  Prospectors,  Min- 
ers, and  Schools.     3d  edition.     St.  Louis,  1881. 
Kunhardt,  W.  B.:   The   Practice  of   Ore  Dressing  in 

Europe.     New  York,  1884. 
Randall,  P.  M,:   The  Quartz  Operator's  Hand  Book. 

Revised  and  enlarged.     New  York,  1871. 
Van  Wagenen,   T.  F.:    Manual  of    Hydraulic    Mining. 

For  the  Use  of  the  Practical  Miner.     New  York, 

1880. 


434  MA  N  UA  L  OF  A  SSA 


Assaying. 

Aaron,  C.  H.:    Assaying.     In    Three    Parts.     Part    I, 

Gold  and  Silver  Ores,  1884;  Parts  II  and  III,  Gold 

and  Silver  Bullion,  Lead,  Copper,  etc.,  1885.     San 

Francisco. 
Balling,  C.  A.  M.:  Die  Probirkunde  des  Eisens  und  der 

Brennmaterialen.     Prag,  1868. 
Balling,  C.  A.  M.:    Die   Probirkunde.      Anleitung  zur 

Vornahme    docimastischer    untersuchungen    der 

Berg-und  Hiitten  producte.     Braunschweig,  1879. 
Bodeman,  Th.,  and  Bruno  Kerl  :    Anleitung  zur  Berg- 

und  Hiittenmannischen  Probirkunde.    2d  edition. 

Clausthal,  1857. 
Bodeman,    Th.,  and  Bruno  Kerl:    A    Treatise    on    the 

Assaying  of  Lead,  Copper,  Silver,  Gold  and  Mer- 

cury.   Translated  by  W.  A.  Goodyear.    New  York, 

1865. 
Chapman,  E.  J.:  Practical  Instructions  for  the  Deter- 

mination by  Furnace  Assay  of  Gold  and  Silver  in 

Rocks  and  Ores.     Toronto,  Can.,  1881. 
KerL  Bruno  :  Metallurgische  Probirkunst.    2d  edition. 

Leipsig,  1882. 
Kerl,  Bruno  :   The  Assayer's  Manual.     Translated  by 

William  T.  Brannt,  edited  by  William  H.  Wahl. 

Philadelphia  and  London,  1883. 
Lieber,  O.  M.:  The  Assayer's  Guide.     Phila.,  1852. 


APPENDIX.  435 


Mitchell,  John:  A  Manual  of  Practical  Assaying. 
Edited  by  Wm.  Crookes.  5th  edition.  New  York, 
1881. 

North,  Oliver :  The  Practical  Assayer.     London,  1874. 

Overman,  F.:  Practical  Mineralogy,  Assaying,  and 
Mining.  Phila.,  1851. 

Phillips,  J.  S.:  The  Explorers' and  Assayers'  Compan- 
ion. San  Francisco,  1879. 

Ricketts,  P.  de  P.:  Notes  on  Assaying  and  Assaying 
Schemes.  New  York,  1879. 

Silversmith,  J.:  A  Practical  Hand -Book  for  Miners, 
Metallurgists,  and  Assayers.  New  York,  1866. 

Triplett,  Frank:  How  to  Assay.     St.  Louis,  1881*. 

Metric  System  ;    Weights  and  Measures. 
Barnard,  F.  A.  P.:  The  Metric  System  of  Weights  and 

Measures.     2d  edition.     New  York,  1872. 
Egleston,  T.:  Tables  of  Weights,  Measures,  Coins,  etc. 

New  York,  1871.  » 

Oldberg,  O.;    Weights,  Measures,  and  Specific  Gravity. 

Chicago,  1885. 

Mining  Law. 

Copp,  H.  N.:  American  Mining  Code.  $d  edition. 
1880. 

*  Besides  the  above,  there  have  been  a  number  of  publications 
from  1741  to  about  1850  which  are  either  obsolete  in  their  teach- 
ings, or  the  information  contained  therein  is  embraced  in  the 
preceding. 


436  MANUAL    OF  ASSAYING. 

Carpenter,  M.  B.:  Mining  Code.     3d  edition.     1880. 

Wade,  W.  P.:  Manual  of  Mining  Law.  St.  Louis, 
1882. 

Wilson,  C.  S.:  Mining  Laws  of  the  United  States,  Col- 
orado, New  Mexico,  and  Arizona.  1881. 

It  is  not  pretended  that  the  above  list  is  complete, 
nor  even  that  it  comprises  all  the  best  works;  it  is 
simply  a  list  of  some  that  are  considered  standard 
authorities  in  their  respective  lines,  save  perhaps  in 
the  department  of  assaying,  where  certain  ones  are 
included  that  are  not  particularly  valuable. 


The  plan  of  an  assay  laboratory,  given  on  the  op- 
posite page,  shows  a  simple  and  convenient  arrange- 
ment, which  can  be  adapted  to  almost  any  room. 


APPENDIX. 


437 


1 

s 

Morta 

Window                                                                            Window 

Table           ^p^1"8 
-^                                                   1  LL 

>  J                                                                                        Window 
r  Block 

Working  Table 

i 

.Assay 
Furnace 

LABOKATOBY 

Window 

Coke  or 
Charcoal  Bin 

Closet 

Window 

Door 
Desk  for  Chemical  Work 

Water 

Water 

Cabinet                          Book  Case 

Window                                                                                                   Door 
OFFICE 

Desk 

Window 

Scale  Shelf 

Window                                                          Window 

438 


MANUAL    OF  ASSAYING. 


FORM    FOR    CERTIFICATE    OF    ASSAY. 

Almost  every  assayer  has  his  own  particular  blank, 
but  so  long  as  the  certificate  states  plainly  the  results 
of  his  work,  any  little  differences  of  detail  are  un- 
important. The  form  given  below  is  about  as  satis- 
factory as  any. 


i  . 

P 

3 
CL       ^ 

•o' 
o 

D 

P 

c/i      a; 

t/i     i 

03     w 

3  £ 

a    » 
o     o 

_g20 

i  "8  a  ?  2. 
•  "  i  a-0- 

po 

;      H 
1      -*i 
;     •< 

I5f*j 

1        n> 

!    s       | 

-•***£ 

Elfl 

<-!•                                  > 

3*                   •< 

m 

:     ^        o 

Rlf*} 

'           f8 

P 

If    ^ 

^Po   «<H 

<§oo^2Lo 
oas:-|cp 

r.  ? 

^o         S 

w 

2.      ?                 0 

o*  2          o 
^    . 

o     r 

Ml 

5'    ?            r 
w     S 
3    5' 

> 

(ft 
v> 

i 

Remarks. 

C/l 

-  s-  M 

«?    %     S 

Of 

1 

APPENDIX.  439 


OUTFIT. 

With  the  following  outfit,  it  is  believed  the 
assayer  can  perform  the  ordinary  crucible  and 
scorification  assays  of  gold,  silver,  copper  and 
lead  ores : 

Hammers,  sledge,  medium  and  small $2  oo 

Iron  mortar  (8  inch  diam.,  i  gal.  capacity)  and 

pestle,  wt.  1 9  Ibs i  25 

Steel  spatulas,  one  large  and  one  small 75 

Sieves,  20,  40  and  100  mesh 2  50 

Hand-scales  for  fluxes 3  oo 

Ore  or  pulp  scales 22  oo 

Assay  balance,  with  weights  (i  grm  down  to 

•fa  mgrm) 65  oo 

Set  gramme  weights,  100  grms  down 6  oo 

Set  assay  ton  weights 6  50 

Furnace,  Brown's  portable 20  oo 

6  muffles,  Battersea  J 8  25 

i  pair  crucible  tongs *  . .  .  i  25 

i  pair  scorifier  tongs i  oo 

i  pair  cupel  tongs i  oo 

Shovel,  scraper  and  hoe 75 

Scorification  mould i  oo 

Crucibles,  S.  T.  U.  V.,  i  doz  each,  .with  covers  4  50 

Crucibles,  Colorado,  2  doz i  10 


440  MANUAL    OF  ASSAYING. 

Scorifiers,  200  2|  inch,  200  2%  inch, 9  50 

Cupels,  4  doz.  i  inch 3  oo 

Cupel  mould 2   25 

Piece  rubber  cloth i   oo 

Alcohol  lamp 50 

Ring  stand i   oo 

Wire  triangle 10 

i  doz.  i  inch  porcelain  capsules 2  oo 

i  doz.  i£  inch  porcelain  capsules 250 

i  quart  wash-bottle 75 

i  pair  3  inch  watch-glasses 50 

Blow-pipe 20 

Magnifying  glass,  pocket  size 75 

Magnet 20 

Small  steel  hammer  and  anvil i   75 

Pair  brass  pincers 25 

Small  cold  chisel   50 

Horn  spoon 25 

1  Ib.  bottle  pure  nitric  acid '50 

2  Ibs.  bi-carbonate  soda  ....    20 

i  Ib.  carbonate  of  potash 20 

\  Ib.  cyanide  of  potash 25 

1  Ib.  borax  glass 50 

2  Ibs.  flour 20 

1  Ib.  argol 1 8 

2  Ibs.  nitre  (nitrate  potash) 30 

2  Ibs.  litharge   -  .  2*5 


APPENDIX.  441 


i  lb.  charcoal,  pulverized $  25 

i  lb.  silica 20 

\  lb.  sheet  lead  25 

1  lb.  granulated  lead 40 

2  Ibs.  bone-ash 36 

i  oz.  pure  silver  foil 75 


$179  64 

Note-books,  gummed  labels,  tin  boxes  for  dry  re- 
agents, bottles,  bags  or  boxes  for  samples,  etc.,  accord- 
ing to  fancy  of  purchaser. 

BLOW-PIPE  OUTFIT. 

Apparatus  for  Blow-piping,  according  to  Prof.  Platt- 
ner,  the  whole  in  elegant  velvet-lined,  polished  ma- 
hogany case,  with  handle  and  lock,  for  travelling, 
complete,  with  case,  $38. 

The  set  includes: 
i  set  of    three    porcelain      i  charcoal    borer,    4   cor- 


dishes. 

i  diamond  steel  mortar. 

i  pair  platinum  pointed 
forceps. 

i  pair  heavy  tip  steel  for- 
ceps. 

i  pair  steel  forceps. 

i  steel  chisel. 


nered,  with  spatula. 

i  charcoal  borer,  club 
shape. 

i  pair  fine  scissors. 

i  wire  holder,  with  3  plat- 
inum wires  in  the  han- 
dle. 

i     Planner's     blow  -  pipe 


442 


MANUAL    OF  ASS  A  YING. 


lamp,  with  patent  swivel, 
nickel-plated. 

i  charcoal  saw. 

i  holder  for  the  mat- 
rasses. 

i  nickel-plated  Plattner's 
blow-pipe. 

i  heavy  platinum  tip  for 
same. 

i  steel  hammer  with  wire 
handle. 

i  set  mould  and  stamps. 

i  pair  of  steel  nippers, 
Plattner's. 

i  dquble  lens. 

i  knife,  ivory  handle. 

i  dropping  pipette. 

i  camel's  hair  brush. 

6  matrasses. 

i  alcohol  lamp,  with  nick- 
el-plated air-tight  top. 

i  chamois  skin. 

6  glass  tubes. 

6  pieces  square-cut  char- 
coal. 


Metal  trays  for  coal,  ashes, 
and  filters. 

1 8  flat-top,  stoppered  and 
labelled  re-agent  bot- 
tles, containing  the  fol- 
lowing re-agents: 

Test  lead. 

Tin. 

Phosphorus  salt. 

Borax  powder. 

Borax  glass. 
|  Boracic  acid,  fused. 

Boracic  acid,  cryst. 

Plattner's  flux. 

Bismuth  flux. 

Carbonate  soda. 

Potash  oxalate. 

Salt. 

Soda  nitrate, 
i  Charcoal. 

Boneash,  sieved. 

Boneash,  washed. 

Copper  oxide. 

Bi-sulphate  potash. 

Test  papers. 


SECTION    III. 
TABLES. 

MULTIPLICATION    TABLE    FOR    GOLD    AND    SILVER. 


- 

SILVER. 

GOLD. 

OUNCES. 

VALUE. 

OUNCES. 

VALUE. 

I 

$1  29 
2  58 

3  87 
5  16 
6  45 
7  74 
9  03 
10  32 
1  1  61 

$20  67 

4i  34 
62  01 
82  68 
103  35 

124  02 
144  69 
105  36 

186  03 

2 

2 

« 

-?  . 

A  .  . 

B 

6  

J  •  ' 

6  

7 

7 

8.   

8   

NOTE  —The  above  table  is  more  relative  than  actual.  $20.00  is  commonly 
used  as  a  factor  for  gold,  and  for  silver  the  value  per  ounce  fluctuates  with 
the  market. 

443 


444 


MANUAL    OF  ASSA  YING. 


TABLE    OF    VALUES    OF    GOLD    AND    SILVER. 


WEIGHT. 

Of  Gold  is 
worth 

Of  Silver  is 
worth 

i  grain  Troy  

$O  0430 

$O  0026 

i  pennyweight  Troy—  24 
grains  Troy  

i.o'?'?q 

o  0646 

i  ounce  Troy  =  20  penny- 
weights Troy  =  480  grains 
Troy  

20  67  18 

I    2O2Q 

i  ounce  Avoirdupois  =  43  y-J- 
grains  Troy  

1  8  841  q 

i.^yy 
I    I  78/1 

i  pound  Troy  =  1  2  ounces  Troy 
=  240  pennyweights  Troy  = 
^,760  grains  Trov.  . 

248.0620 

1.1   J  UZJ. 

1C  C  i  e  i 

i  pound  Avoirdupois  =  16 
ounces  Avoirdupois  =  7,000 
grains  Troy  

-7QI    d.6A2 

1  8  8551 

i    ton    Avoir.  =  2,000    pounds 

Avoir  _  (  29,166  ounces  Troy    (  _ 
~   1  32,000  ounces  Avoir,  j 

14,000,000  grains  Troy  .... 

6O2    O28    4660 

•27  710  ^84.6 

NOTE. — The  above  values  are  figured  on  the  basis  of  $20.67  Per 
Troy  oz.  for  gold,  and  $1.29  for  silver.  Were  the  factors  made  $20 
for  gold,  and  the  fluctuation  prices  of  $i.ioand  $1.15  for  silver,  the 
values  given  would  be  varied  considerably. 


APPENDIX.  445 


TABLES   OF  WEIGHTS. 

AVOIRDUPOIS    WEIGHT. 

16  Drams=:i   Ounce. 
1 6  Ounces  =  i   Pound. 
28  Pounds^  i   Quarter.* 
4Quarters=i   Hundredweight. 
20  Hundred  weight=i  Ton  of  2240  pounds. 

AVOIRDUPOIS    WEIGHT. 

i   dram. 

i  ounces  16  drams, 
i  pound=  16  ounces=  256  drams, 
i   quarter=28  pounds=448  ounces  =  7i68  drams, 
i  h'dwt  =  4  quarters=ii2  pounds=iy92  ounces=  28672 
v      drams. 

i  ton=2o  h'dwt— 80  quarters  —  2240    pounds  =  35840 
ounces =5  7 3440  drams. 

AVOIRDUPOIS    WEIGHT. 

25   Pounds=i   Quarter. 
4  Quarters^  i   Hundred  weight. 
20  Hundred  weight^i  Ton  of  2000  pounds. 

AVOIRDUPOIS    WEIGHT. 

i  quarter=  25  pounds  =  4oo  ounces=64oo  drams. 

*  In  some  parts  of  the  United  States. 


446  MANUAL    OF  ASSAYING. 

i  h'dwt— 4    quarters  ~ioo     pounds  =1600    ounces  = 

25600  drams. 
i  ton  =  2o  hdwt=8o    quarters  =  2000    pounds  =  32000 

ounces:=5i2ooo  drams. 

TROY    WEIGHT. 

24  Grains=i   Pennyweight. 
20  Pennyweights— i   Ounce. 
12  Ounces=n   Pound. 

TROY    WEIGHT. 

i  grain. 

i  pennyweight  =  24  grains. 

i  ounces  20  penny  weights^  480  grains. 

i  pound  =12  ounces=24o  pennyweights=576o  grains. 

APOTHECARIES'  WEIGHT. 

20  Grains=i  Scruple. 

3  Scruples^:   Dram. 

8  Drams^i   Ounce. 

12  Ounces=i   Pound. 

APOTHECARIES'  WEIGHT. 
i   grain. 

i   scruple=2o  grains, 
i  dram  =  3  scruples=6o  grains, 
i  ounce= 8  drams=24  scruples=48o  grains, 
i  pounds  1 2   ounces  =  96   drams=288    scruples  =  576o 
grains. 


APPENDIX. 


447 


i   pound,  Troy,  =5760  grains. 

i   pound,  Apothecaries',          =5760  grains, 
i   pound,  Avoirdupois,  =7000  Troy  grains. 

FRENCH    OR    METRIC    SYSTEM    OF    WEIGHTS. 

i   Milligramme    —.001  of  a  Gramme. 

i   Centigramme  =.oi  "  " 

i   Decigramme     =.i  "  " 

i   Gramme  =     i  Gramme. 

i   Decagramme   —     10        Grammes. 

i   Hectogramme^     100 

i   Kilogramme     =     1000 

i   Myriagramme  =     10000 

or 

10  Milligrammes  (mgrs)  =  i  Centigramme  (cgr). 
10  Centigrammes  =  i   Decigramme  (dgr). 

10  Decigrammes  =i   Gramme  (grm). 

10  Grammes  ==i   Decagramme  (dkgr). 

10  Decagrammes  =  i   Hectogramme  (hgr). 

10  Hectogrammes  =i   Kilogramme  (kgr). 

10  Kilogrammes  =  i   Myriagramme(myrgr). 


i   mgr. 

i  cgr.  =  10  rrigrs. 
i   dgr.  =  io  cgrs.  =  ioo  mgrs. 
i  grm.  =  10  dgrs.  =  ioo  cgrs.=  i,ooo  mgrs. 
i  dkgr.=  10    grins.  =  100    dgrs.=  1,000    cgrs.=  10,000 
mgrs. 


44-8  MANUAL   OF  ASSA  YING. 

i  hgr.=  io    dkgrs.=  ioo    grms.=  1,000    dgrs.=  10,000 

cgrs.— 100,000  mgrs. 
i   kgr.=rio    hgrs.=  ioo    dkgrs.=  1,000    grms.=  10,000 

dgrs.  =  100,000  cgrs.  =  1,000,000  mgrs. 
i   myrgr.  =  io    kgrs.z=ioo   hgrs.=  i,ooo    dkgrs.=:  10,000 

grms.  =  ioo,ooo   dgrs.  =  i,ooo,ooo   cgrs.  =  10,000,000 

mgrs. 

i  gramme=  15.43235  Troy  grains. 


APPENDIX. 


449 


EQUIVALENTS    OF    SOME    OF    THE 

ENGLISH  AND    FRENCH 

WEIGHTS.* 

Troy  Grains. 

Grammes. 

i 

.064798 

2                    := 

•129697 

3              = 

.194396 

4 

•259!95 

r                      — 

•323994 

6              — 

388793 

*j              — 

•453592 

8              = 

•518391 

9              = 

•583190 

Grammes. 

Troy  Grains. 

i              — 

I5-43235 

2                   =^ 

30.86470 

3 

46.29705 

4 

61.72940 

r                    — 

77.16175 

6              = 

92.59410 

7 

108.02645 

8              = 

123.45880 

9 

138.89115 

T.  Egleston's  Tables  of  Weights,  Measures,  Coins,  etc.,  p.  24. 


450 


MANUAL   OF  ASSAYING, 


ASSAY    TON    EQUIVALENTS    IN    GRAMMES,  TROY 
GRAINS,   AND    TROY    OUNCES. 

Based  on  i  gramme  =  i5. 43235  Troy  grains;  hence  i  assay  ton 
or  29.166  grammes  =  i5. 43235  x  29.166=450.09992  Troy  grains. 


Assay 
Tons. 

Value  in 
Grammes. 

Value  in 
Troy  Grains. 

Value  in 
Troy  Ounces. 

0.05 

1.458 

22.504 

• 

0.10 
0.15 

2.916 
4.374 

45.009 
67.514 

0.20 

5.833 

90.019 

0.25 

7.291 

112.524 

0.30 

8.749 

135.029 

0.35 

10.208 

157.534 

0.40 

11.666 

180.039 

0.45 

13.124 

202.544 

0.50 

14.583 

225.049 

0.55 

16.041 

247.554 

0.60 

17.499 

270.059 

0.65 

18.958 

292.564 

0.70 

20.416 

315.069 

0  75 

21   874 

337  574 

0.80 

23  333 

360.079 

0.85 

24  791 

382  584 

0.90 

26  249 

405.089 

0.95 

27.708 

427.594 

1.00 

29.166 

450.099 

APPENDIX. 


451 


ASSAY    TON    EQUIVALENTS CONTINUED. 


Assay 
Tons. 

Value  in 
Grammes. 

Value  in 
Troy  Grains. 

Value  in 
TroyOunces. 

1.05 

30.624 

472.604 

1.10 

32.083 

495.109 

1  .  032 

1.15 

33.541 

517.614 

1.078 

1.20 

34.999 

540.119 

1.125 

1.25 

36.458 

562.624 

1.173 

1.30 

37.916 

585.129 

1.219 

1.35 

39.374 

607.634 

1.266 

1.40 

40.833 

630.139 

1.313 

1.45 

42.291 

652.644 

1.360 

1.50 

43.749 

675.149 

1.407 

1  .55 

45.208 

697.654 

1.453 

1.60 

46.666 

720.159 

1.500 

1.65 

48.124 

742.664 

1.547 

1.70 

49.583 

765.169 

1.594 

1.75 

51.041 

787.674 

1.641 

1.80 

52.499 

810.179 

1.667 

1.85 

53.958 

832.684 

1.735 

1.90 

55.416 

855.189 

1.782 

1.95 

56.874 

877.694 

1.829 

2.00 

58.333 

900.199 

1.875 

452 


MANUAL    OF  ASSAYING. 


ASSAY    TON    EQUIVALENTS CONTINUED. 


Assay 
Tons. 

Value  in 
Grammes. 

Value  in 
Troy  Grains. 

Value   in 
Troy  Ounces. 

2.05 

59.791 

922.704 

1.922 

2.10 

61.249 

945.209 

1.969 

2.15 

62.708 

967.714 

2.016 

2.20 

64.166 

990.219 

2  .  063 

2.25 

65.624 

1012.724 

2.110 

2.30 

67.083 

1035.229 

2.157 

2.35 

68.541 

1057.734 

2.204 

2.40 

69.999 

1080.239 

2.250 

2.45 

71.458 

1102.744 

2.297' 

2.50 

72.916 

1125.249 

2.344 

2.55 

74.374 

1147.754 

2.391 

2.60 

75.833 

1170.259 

2.438 

2.65 

77.291 

1192.764 

2.485 

2.70 

78.749 

1215.269 

2.531 

2.75 

80.208 

1237.774 

2.579 

2.80 

81.666 

1260.279 

2.626 

2.85 

83.124 

1282.784 

2.672 

2.90 

84.583 

1305.289 

2.719 

2.95 

86.041 

1327.794 

2.766 

3.00 

87.499 

1350.299 

2.813 

APPENDIX. 


453 


ASSAY    TON    EQUIVALENTS CONTINUED. 


Assay 
Tons". 

Value  in 
Grammes. 

Value  in 
Troy  Grains. 

Value  in 
Troy  Ounces. 

3.05 

88.958 

1372.804 

2.860 

3  .  10 

90.416 

1395.309 

2  .  905 

3.15 

91.874 

1417.814 

2.954 

3  .  20 

93.333 

1440.319 

3.001 

3.25 

94.791 

1462.824 

3.048 

3.30 

96.249 

1485.329 

3.094 

3.35 

97  .  708 

1507.834 

3.141 

3  .  40 

99.166 

1530.339 

3.188 

3.45 

100.624 

1552.844 

3.235 

3.50 

102.083 

1575.349 

3.282 

3.  55 

103  .  541 

1597.854 

3.329 

3.60 

104.999 

1620.359 

3.376 

3.65 

106.458 

1642.864 

3  .  423 

3.70 

107.916 

1665.369 

3.470 

3.75 

109.374 

1687.874 

3.516 

3.80 

110.833 

1710.379 

3.563 

3.85 

112.291 

1732.884 

3.610 

3.90 

113.749 

1755.389 

3.657 

3.95 

115.208 

1777.894 

3.704 

4.00 

116.666 

1800.399 

3.751 

454 


MA  N  UA  L    OF  A  SSA  YING. 


ASSAY    TON    EQUIVALENTS CONTINUED. 


Assay 
Tons. 

Value  in 
Grammes. 

Value  in 
Troy  Grains. 

Value  in 
Troy  Ounces. 

4.05 

118.124 

1822.904 

3.798 

4.10 

119.583 

1845.409    !     3.845 

4.15 

121.041 

1867.914 

3.891 

4.20 

122.499 

1890.419 

3  .  938 

4.25 

123.958 

1912.924 

3  .  985 

4.30 

125.416 

1935.429 

4.032 

4.35 

126.874 

1957.934 

4.079 

4.40 

128.333 

1980.439 

4.126 

4.45 

129.791 

2002  .  944 

4.173 

4.50 

131.249 

2025  .  449 

4.220 

4.55 

132  .  708 

2047.954 

4.267 

4.60 

134.166 

2070.459 

4.313 

4.65 

135.624 

2092  .  964 

4.360 

4.70 

137  .  083 

2115.469 

4.407 

4.75 

138.541 

2137.974 

4.454 

4.80 

139.999 

2160.479 

4  .  500 

4.85 

141  .  458 

2182.984 

4.548 

4.90 

142.916 

2205.489 

4.595 

4.95 

144.374 

2227  .  994 

4.642 

5.00 

145  .  833 

2250.499 

4.689 

APPENDIX. 


455 


ASSAY    TON    EQUIVALENTS CONTINUED. 


Assay 
Tons. 

Value  in 
Grammes. 

Value  in 
Troy  Grains. 

Value  in 
Troy  Ounces. 

5.05 

5.10 

147.291 
148  .  749 

2273.004 
2295.509. 

4.735 

4.782 

5.15 

150.208 

2318.014 

4.829 

5.20 

151.666 

2340.519 

4.876 

5.25 

153.124 

2363  .  024 

4.923 

5.30 

154.583 

2385.529 

4  .  970 

5.35 

156.041 

2408  .  034 

5.017 

5.40 

157.499 

2430.539 

5  .  0(54 

:>  .  45 

158.958 

2453  .  044 

5.111 

5.50 

160.416 

2475  .  549 

5.157 

5.55 

161.874 

2498  .  054 

5  .  204 

5  .  60 

163.333 

2520.559 

5  .  251 

5.65 

164.791 

2543.064 

5  .  298 

5.70 

166.249 

2565  .  569 

5.345 

5.75 

167.708 

2588  .  074 

5.392 

5.80 

169.166 

2610.579 

5  .  439 

5.85 

170.624 

2633.084 

5.486 

5.90 

172.083 

2655.589 

5  .  532 

5.95 

173.541 

2678.094 

5.579 

6.00 

174.999 

2700.579 

5.626 

456 


MANUAL    OF  ASS  A  YING. 


ASSAY    TON    EQUIVALENTS CONTINUED. 


Assay 
Tons. 

Value  in 
Grammes. 

Value  in 
Troy  Grains. 

Value  in 
TroyOunces. 

6.05 

176.458 

2723.084 

5.673 

6.10 

177.916 

2745.589 

5.720 

6.15 

179.374 

2768.094 

5.767 

6.20 

180.833 

2790.599 

5.814 

6.25 

182.291 

2813.104 

5.861 

6.30 

183.749 

2835.609 

5.908 

6.35 

185.208 

2858.114 

5.954 

6.40 

186.666 

2880.619 

6.001 

6.45 

188.124 

2903.124 

6.048 

6.50 

189.583 

2925.629 

6.095 

6.55 

191.041 

2948.134 

6.142 

6.60 

192.499 

2970.639 

6.189 

6.65 

193.958 

2993.144 

6.236 

6.70 

195.416 

3015.649 

6.283 

6.75 

196.874 

3038.154 

6.329 

6.80 

198.333 

3060.659 

6.376 

6.85 

199.791 

3083.164 

6.423 

6.90 

201.249 

3105.669 

6.470 

6.95 

202.708 

3128.174 

6.517 

7.00 

204.166 

3150.679 

6.564 

APPENDIX. 


457 


ASSAY    TON    EQUIVALENTS CONTINUED. 


Assay 
Tons. 

Value  in 
Grammes. 

Value    in 
Troy  Grains. 

Value  in 
Troy  Ounces. 

7.05 

205.624 

3173.184 

6.611 

7.10 

207.083 

3195.689 

6.658 

7.15 

208.541 

3218.194 

6.705 

7  .  20 

209.999 

3240.699 

6.751 

7.25 

211.458 

3263.204 

6.798 

7.30 

212.916 

3285.709 

6.845 

7.35   v 

214.374 

3308.214 

6.892 

7.40 

215.833 

3330.719 

6.939 

7.45 

217.291 

3353.224 

6.986 

7.50 

218.749 

3375.729 

7.033 

7.55 

220.208 

3398.234 

7.080 

7.60 

221.666 

3420.739 

7.127 

7.65 

223.124 

3443  .  244 

7.173 

7.70 

224.583 

3465.749 

7.220 

7.75 

226.041 

3488.254 

7.267 

7.80 

227.499 

3510.759 

7.314 

7.85 

228.958 

3533.264 

7.361 

7.90 

230.416 

3555.769 

7.408 

7.95 

231.874 

3578.274 

7.455 

8.00 

233.333 

3600.779 

7.502 

458 


MA NUAL    OF  A  SSA  YING. 


ASSAY    TON    EQUIVALENTS CONTINUED. 


Assay 
Tons. 

Value  in 
Grammes. 

Value  in 
Troy  Grains. 

Value  in 
TroyOunces. 

8.05 

234.791 

3623.284 

7.54',) 

8.10 

236.249 

3645  .  789 

7  .  595 

8.  15 

237.708 

3668.294 

7.642 

8.20 

239.166 

3690.799 

7.689 

8.25 

240  .  624 

3713.304 

7.736 

8.30 

242.083 

3735  .  809 

7.783 

8.35 

243.541 

3758.314 

7.830 

8.40 

244.999 

3780.819 

7.877 

8.45 

246.458 

3803  .  324 

7.924 

8  .  50 

247.916 

3825.829 

7.970 

8.55 

249.374 

3848  .  334 

8.017 

8.60 

250.833 

3870  .  839 

8.064 

8.65 

252.291 

3893  .  344 

8.111 

8.70 

253.749 

3915.849 

8.158 

8.75 

255  .  208 

3938.354 

8  .  205 

8.80 

256.666 

3960  .  859 

8.252 

8.85 

258.124 

3983  .  364 

8  .'299 

8.90 

259.583 

4005  .  869 

8.346 

8.95 

261  .  041 

4028  .  374 

8.392 

9.00 

262  .  449 

4050.879 

8.439 

APPENDIX. 


459 


ASSAY    TON    EQUIVALENTS  CONTINUED. 

Assay 
Tons. 

Value  in 
Grammes. 

Value  in 
Troy  Grains. 

Value  in 
Troy  Ounces. 

9.05 

263  .  958 

4073.384 

8.486 

9.10 

265.416 

4095.889 

8.533 

9.15 

266.874 

4118.394 

8.580 

9.20 

268.333 

4140.899 

8.627 

9.25 

269.  79L 

4163.404 

8.674 

9  .  30 

271.249 

4185.909 

8.721 

9.85 

272.708 

4208.414 

8.768 

9  .  40 

274.166 

4230.919 

8.814 

9.45 

275.624 

4253.4-24 

8.861 

9.50 

277.083 

4275.929 

8.908 

9  .  55 

278.541 

4298  .  434 

8.955 

9.60 

279.999 

4320.939 

9.002 

9.65 

281.458 

4343.444 

9.049 

9.70 

282.916 

4365  .  949 

9.096 

9.75 

284.374 

4388.454 

9  .  143 

9.80 

285.833 

4410.959 

9.189 

9.85 

287.291 

4433  .  464 

9.236 

9.90 

288.749 

4455  .  969 

9.283 

9.95 

290.208 

4478.474 

9.330 

10.00 

291.666 

4500.979 

9.377 

INDEX. 


AARON,  references  to,  142,  264, 
265,  267,  280,  281,  282,  293,  296, 
298,  301,  302,  332,  367,  434. 

AARON'S  ASSAYING,  434. 

ACETATE  OF  LEAD,  re-agent,  141. 

ACETIC  ACID,  re-agent,  144. 

ACICULAR  BISMUTH,  mineral,  422. 

ACID,  ACETIC,  re-agent,  144. 

ACID,  CITRIC,  re-agent,  146. 

ACID  FLUXES,  225,  227;  silica,  129, 
137- 

ACID  GANGUES,   225,   227. 

ACID,  HYDROCHLORIC  (muriatic), 

147. 
ACID,  NITRIC,  re-agent.  143,  148; 

preparation    of    various 

strengths,    211;    to   free   from 

chlorine,  143. 

ACID,  SULPHURIC,  re-agent,  151. 
ACID,  TARTARIC,  re-agent,  151. 
ACTINIUM,  element,  14. 
AIKINITE,  mineral,  418,  422. 
AINSWORTH  balance,  51. 
ALABANDITE,  231. 
ALASKAITE,  mineral,  418,  425. 
ALCOHOL,  re-agent,  144. 
ALDEN  CRUSHER,  24. 
ALGODONITE,  mineral,  421,  422. 


ALPHABETS  AND  FIGURES,  steel, 
126. 

ALTAITE,  mineral,  418,  421,  425. 

ALUMINA,  and  lead  phosphate, 
mineral,  427;  crucibles,  103. 

ALUMINIUM,  element,  13. 

AMALGAMATION,  assay,  351;  mor- 
tar, 33. 

AMALGAM,  gold,  mineral,  417. 

AM.  INST.  MIN.  ENG.,  reference 
to,  334- 

AMMONIA,  aqua  (caustic,  hydrate, 
water),  144;  carbonate,  129,135, 
145;  citrate,  146. 

ANALYSIS,  books  on,  429;  blow- 
pipe, books  on,  431;  copper 
ores,  333;  definition,  15;  re- 
agents for,  144;  volumetric, 
books  on,  430 

ANGLESITE,  mineral,  425. 

ANNEALING  CUPS,  no;  plate,  no. 

ANTIMONIAL  ores,  188,  219;  red 
silver  ore,  168,  420;  silver,  419; 
sulphide  of  silver  and  lead,  419, 
426. 

ANTIMONY,    and    lead    sulphide, 

425;  and   silver  sulphide,   168, 

420;  arsenic  and  silver  sulphide, 

168,  419 ;  bismuth  and  lead  sul- 

461 


462 


INDEX. 


phide,  426;  copper  and  lead 
sulphide,  422,  425  ;  cupel  color, 
192;  element,  13;  gray,  232, 
249;  in  copper  ores,  349;  met- 
al, 16;  native,  421;  oxide,  420; 
qualitative  scheme  for,  240; 
sulphuret,  232;  vapors,  235. 

ANVILS,  and  methods  of  mount- 
ing, 119. 

APOTHECARIES'  weights,  tables 
of,  446. 

APPARATUS,  for  analysis  and  as- 
saying, 19;  glass  and  porcelain, 
in;  graduated,  114;  miscella- 
neous, 116;  sulphuretted  hy- 
drogen, 150;  used  in  furnace, 

IO2. 

APPENDIX,  325. 

AQUA  AMMONIA.,   re-agent,  144. 

ARGENTIFEROUS,  gold,  417,  419; 

gray   copper,    169;    lead   ores, 

169;    ores,    168;    pyrites,    170; 

zinc  blende,  170. 
ARGENTIC  NiTRATE,re-agent,i48. 
ARGENTITE,    mineral,    232,    238, 

418. 
ARGOL,  re-agent,    128,    133,  222; 

reducing  power,  161. 
"  ARRASTRE,"  33. 
ARSENATE,  LEAD,  mineral,  426. 
ARSENIC,    antimony    and    silver 

sulphide,  168,  419;  cupel  color, 

192;    element,    13;    in    copper 

ores,  348,  350;  native,  418,  421; 

sulphuret,  232;  vapors.  235. 
ARSENICAL,    copper,    423;     ores, 

188,  219;  silver  ore,  168,  419. 


ARSENIDE,  COPPER,  mineral,  422, 
423,  425- 

ARSENOPYRITE,  or  arsenical  iron 
pyrites,  mineral,  167,  231,  235, 
238,  249,  418,  421. 

ASH,  BONE,  152. 

ASSAY,  amalgamation,  351;  base 
bullion,  404;  certificate,  438; 
chlorination,  364;  copper,  305; 
crucible,  methods  of,  264;  ga- 
lena, 312;  gold  and  silver,  170; 
gold  and  silver  bullion,  369; 
laboratory,  plan  of,  437;  lead, 
312;  ton  equivalents,  450;  ton 
weights,  and  explanation,  60. 

ASSAYING,  apparatus,  19;  books 
on,  434;  definition,  15;  dry  re- 
agents for,  128;  free  gold  and 
silver  ores,  329;  methods  of, 
180;  of  various  minerals  in  an 
ore,  327;  outfit,  439;  re-agents 
used  in,  128,  wet  re-agents 
used  in,  142. 

"  ASTONISHING,"  173. 

ATACAMITE,  mineral,  422. 

ATTWOOD,  blow-pipe  assaying, 
431;  reference  to,  13,  357. 

AURICHALCITE,  mineral,  422. 

AURIFEROUS  SULPHURETS,  167. 

AUSTIN,  L.  S.,  references  to,  172, 
406. 

AVERAGE  SAMPLES,  obtaining  of, 
172. 

AVOIRDUPOIS  to  troy  weights, 
tables  of,  399. 

AVOIRDUPOIS  WEIGHTS,  tables  of, 
445- 


INDEX. 


463 


AZURE  COPPER  ORE  (azurite), 
mineral,  301,  305,  422. 

B 

BALANCES,  Ainsworth,  51,  52; 
Becker,  44,  45,  48;  bullion,  44; 
for  weighing  gold  and  silver 
beads,  44;  Oertling,48;  special 
directions  for,  54;  Troemner, 
44,  45,  46,  47,  48. 

BALLING'S  Works   on  Assaying, 

434- 

BARIUM,  chloride  (muriate),  re- 
agent, 146;  element,  13. 

BARKER'S  ELEMENTARY  CHEMIS- 
TRY, 428. 

BARNARD'S  METRIC  SYSTEM,  435. 

BARNHARDITE,  mineral,  299,  421, 
422. 

BASE  BULLION,  assay,  404;  sam- 
pling, 406. 

BASIC  FLUXES,  129  135,  225,  227. 

BASIC  GANGUES,  225,  227. 

BATEA,  357. 

BATHS,  sand,  122. 

BATTERSEA,  crucibles,  104-5;  fur- 
naces, 84;  muffles,  102;  roast- 
ing dishes,  105;  scorifiers,  106. 

BATTERY,  Bunsen  carbon,  338; 
"gravity,"  340. 

BEADS,  gold  and  silver,  balance 
for  weighing,  44;  inquarting, 
183;  parting,  183;  weighing, 
183,  209. 

BEAKERS,  glass,  114. 

BEAUFAY  CRUCIBLES,  103-4. 


BECKER'S  BULLION  BALANCES,  44, 
45,  48;  pulp  scales,  38. 

BERINGER,  C.  and  J.  J .,  refer- 
ence to,  351. 

BI-CARBONATE  OF  SODA,  re-agent, 
128,  129,  222;  properties,  129. 

BI-CHROMATE  OF  POTASH,  re- 
agent, 14*5,  222. 

BISMUTH,  acicular  (cupreous), 
422;  cupel  color,  192;  element, 
13;  in  copper  ores,  349,  350; 
lead  and  antimony  sulphide, 
426;  metal,  16;  native,  418, 
421;  scorifier  color,  191;  silver, 
420,  427;  silver  and  lead  sul- 
phide, 418.  420,  425,  427;  sul- 
phuret,  232. 

BISMUTHINITE,  mineral,  418. 

BI-SULPHURET,  or  bi-sulphide  of 
iron,  283. 

BI-TARTRATE  OF  POTASH,  re- 
agent, 128,  133,  161. 

BLACK,  flux  substitute,  128,  133; 
copper  or  oxide  of  copper,  233, 
301,  304,  424;  glazed  paper, 
117;  oxide  of  manganese,  re- 
agent, 145 ;  oxide  of  manga- 
nese, mineral,  233;  silver,  420; 
tellurium,  417,  427. 

"  BLACK  JACK,"  231. 

BLACK  LEAD  CRUCIBLES,  103. 

BLAKE  CRUSHER,  24. 

BLENDE,  167,  188,  231,  238,  249; 
argentiferous,  170. 

"  BLICKING,"  205. 

"  BLOSSO'MING,"  207. 

BLOTTING  PAPER,  117. 


464 


INDEX. 


BLOW  PIPE,  123;  analysis,  books 

on,  431 ;  outfit,  441. 
BLUE  carbonate  of  copper  (blue 

malachite,  mountain  blue),  301, 

305,  422,  423. 

BLUE  COPPER,  mineral,  423. 
BLUE  VITRIOL,  mineral,  423. 
BODEMANN  &  KERL'SJ  works  on 

assaying,    434;     reference    to, 

310. 

BOILING  FLASKS,  113. 
BONE-ASH,  152. 
BOOKS,  note,  116;  list  of  useful, 

428. 

BORAX,  128,  131;  glass,  prepara- 
tion of,  132;  re-agent,  128,  131, 

222. 
BORNITE,  mineral,  232,  238,  299, 

421,  422. 

BORON,  element,  13. 
BOSWORTH  CRUSHER,  27. 
BOTTLE  WASH,  112. 
BOTTLES,  re-agent,  in;  sample, 

in. 
BOULANGERITE,     mineral,     421, 

425- 
BOURNONITE,  mineral,   299,  422, 

425- 

BOWIE,  A.  J.,  Treatise  on  Hy- 
draulic Mining,  433. 

BOXES,  SAMPLE,  117,  172. 

BOYER,  C.,  reference  to,  6. 

BRIEF  SCHEME  FOR  SILICA,  iron, 
and  manganese,  413. 

"BRIGHTENING,"  205. 

BRITTLE  SILVER  ORE,  mineral, 
168,  420. 


BROCHANTITE,  mineral,  422. 
BROMIC  SILVER  (bromide  of  sil- 
ver, bromyrite),  169,  418. 
BROMINE,  element,  13;  re-agent, 

145- 

BROWN'S  ASSAY  FURNACE,  86. 

BRUSHES,  118. 

BRUSH'S  MINERALOGY,  431. 

BUCKING  HAMMER,  29. 

BUFFALO  DENTAL  MFG.  Co.,  66, 
78. 

BULLION,  balances,  44;  base,  as- 
say of,  404;  gold  and  silver, 
assay  of,  369;  punch,  126. 

BUNSEN,    battery,    338;    burners, 

122. 

BURETTE,  114;  stands,  127. 


CADMIUM,  element,  13;  cupel 
color,  192;  scorifier  color,  191. 

CESIUM,  element,  14. 

CAIRNS'  QUANTITATIVE  ANALY- 
SIS, 429. 

CALAVERITE,  mineral,  417,  421. 

CALCIUM,  chloride,  146;  element, 
13;  hydroxide,  147. 

CALC-SPAR,  mineral,  278. 

CALCULATIONS  in  scorification 
process,  183,  216. 

CALEDONITE,  mineral,  423,  425. 

GALLON'S  LECTURES  ON  MINING, 

431- 

CAPSULES,  porcelain,  112. 

CARBON,  element,  13. 

CARBONATE,  of  ammonia,  re- 
agent, 129,  135,  145;  of  copper, 


INDEX. 


465 


blue  and  green,  minerals,  301, 
305,  422,  424;  of  lead,  mineral, 
170,  312,  425 ;  of  lead,  re-agent, 
141 ;  of  potash,  re-agent,  128, 
130,  222;  of  sodium,  re-agent, 
145,  222;  of  zinc  and  copper, 
mineral,  422. 

"CARBONATE  ORES,"  167,    187. 

CARBONATES,  tests  for,  408. 
"CARBONS,  PEPPER,"  394. 
CARPENTER'S  MINING  CODE,  436. 
CARROLLITE,  mineral,  299,  423. 
CASE,  GLASS,  for  pulp  scale,  38. 
CASSEROLE,  115. 
CAUSTIC   ammonia,    144;    lunar, 

148;  potash,  146;  soda,  146. 
CERARGYRITE,  mineral,  419. 
CERIUM,  element,  14. 
CERTIFICATE     OF    ASSAY,     form 

for,  438. 

CERUSE,  re-agent,  141. 
CERUSSITE,    mineral,    170,    312, 

421,  425. 

CHALCANTHITE,  mineral,  423. 
CHALCOCITE,  mineral,  232,   238, 

298,  305,  423. 
CHALCOPYRITE,      mineral,     232, 

238,  299,  305,  418,  421,  423. 
CHALK,  dry,  152;  wash,  152. 
CHAMOIS  SKIN,  127. 
CHAPMAN'S  crucible  flux,  279. 
CHAPMAN,  references  to,  173,  279. 
CHAPMAN'S  FURNACE  ASSAY,  434. 
CHARCOAL,    WOOD,     charge    for 

testing,  162;  properties  of,  135, 

re-agent,    135,     222;    reducing 

power,  134,  162. 


CHARGES,  Aaron's  general,  280, 
281;  Chapman's,  279;  crucible 
for  galena,  303;  crucible  for 
quartz,  sand,  or  "dry  ores," 
281,  282;  for  argol,  161 ;  for 
charcoal,  162;  for  chlorides, 
187;  for  copper  mattes,  186; 
for  copper  oxides  and  carbon- 
ates, 307;  for  copper  oxides, 
302;  for  cream  of  tartar,  161; 
for  "dry  ores,"  282;  for  gran- 
ulated lead,  158;  for  iron  oxide, 
297,  298;  for  iron  pyrites,  285, 
289,  291,  292,  293;  for  lead 
carbonates,  321;  for  lead  in 
galena,  312,  315,  316,  317,  319; 
for  lead  oxides,  321;  for  lith- 
arge, 154;  for  native  copper, 
306;  for  nitre,  163;  for  ordin- 
ary scorifications,  185;  for  ox- 
ides of  iron,  187;  for  sulphur- 
ets  of  copper,  300,  308 ;  for 
tellurides,  188;  Mitchell's,  for 
all  gold  and  silver  ores,  277; 
for  testing  ores,  242,  251;  gen- 
eral, for  crucible,  276;  in  scor- 
ification  process,  185;  prelim- 
inary, to  determine  oxidizing 
power,  251;  preliminary,  to 
determine  reducing  power,  242; 
preparation  of,  in  scorification 
process,  183;  scorification  for 
arsenical  and  antimonial  ores, 
188;  for  blende,  188;  for  "  car- 
bonate "  ores,  187;  for  "chlor- 
ide" ores,  187;  for  copper 
glance  or  pyrites,  185;  for  cop- 


466 


INDEX. 


per  matte,  186;  for  "every- 
day "  ores,  185 ;  for  galena, 
187;  for  gray  copper  ore,  186; 
for  native  gold  or  silver,  189, 
for  oxide  of  iron,  187;  for  sul- 
phurets  of  iron,  186;  for  tellu- 
rides,  188;  special,  282; 
Stone's,  278. 

"CHECKING,"  109. 

"  CHECKS,"  390. 

CHEMICAL  TECHNOLOGY,"  Wag- 
ner's, 428. 

CHEMISTRY,  Barker's,  428;  gen- 
eral books  on,  428;  Miller's, 
428;  reference  books  on,  428; 
Roscoe  and  Schlorlemmer,  428; 
Roscoe's  Elementary,  429;  the- 
oretical text-books  on,  428; 
Watts'  Dictionary,  428. 

CHEM.  NEWS,  reference  to,  351. 

CHISEL,  cold,  126. 

CHLORIDE,  and  phosphate  of  lead, 
427;  basic,  146;  calcic,  146; 
mercuric,  148;  of  silver,  169, 
419;  sodic,  135;  stannous,  149. 

"CHLORIDE  ORES,"  169,  187,  219. 

CHLORINATION  assay  of  gold  ores, 
364;  test  for  silver,  367. 

CHLORINE,  element,  13;  in  dis- 
tilled water,  142;  to  free  nitric 
acid  from,  143. 

CHLORO-BROMIDE  OF  SILVER, 
mineral,  219,  419. 

CHROMATE  OF  COPPER  AND  LEAD, 
mineral,  425,  427. 

CHROMIUM,  element,  13;  colors 
in  cupel  and  scorifier,  192, 


CHRYSOCOLLA,  mineral,  226,  302, 

423- 

"CHURNING,"  212. 

CITRATE  OF  AMMONIUM,  re-agent, 
146. 

CITRIC  ACID,  re-agent,  146. 

CLASSEN'S  QUANTITATIVE  ANAL- 
YSIS, 429. 

CLASSIFICATION  of  ores  in  assay- 
ing, 219;  of  silver  ores,  168. 

CLAY,  crucibles,  104;  crucibles, 
French,  103,  104;  lute,  152. 

CLOCK-GLASSES,  112. 

CLOTH,  oil  and  rubber,  117. 

COAL,  reducing  power  of,  134, 
162. 

COATES,  R.  G.,  reference  to,  6, 
364- 

COBALT,  colors  in  cupel  and  scor- 
ifier, 193;  element,  13;  in  cop- 
per ores,  347;  metal,  16;  nickel 
and  copper  sulphide,  423. 

COFFEE-MILL,  133. 

COKE,  reducing  power  of,  134, 
162. 

COLD  CHISEL,  126. 

COLLINS'  MINING  AND  QUARRY- 
ING, 433. 

COLORADO  crucibles,  105;  min- 
erals, 427. 

COLORADOITE,  mineral,  418,  421. 

COLOR  TESTS,  cupel,  190;  scori- 
fier, 190. 

"  COLORS,"  351. 

COLUMBIUM,  element,  14. 

COMMON  SALT,  re-agent,  129. 
135- 


INDEX. 


467 


"CONCENTRATES,"  285. 

COPP'S  MINING  CODE,  435. 

COPPER,  analysis,  methods,  333  ; 
and  antimony,  232;  and  iron 
sulphide,  sulphuret  or  py- 
rites, 232,  299,  305,  422,  423; 
and  lead  chromate,  425,  427, 
and  silver  sulphide  or  sulphur- 
et, 169,  420,  424;  and  uranium 
phosphate,  424;  and  zinc  car- 
bonate, 422 ;  argentiferous 
gray,  169;  arsenical,  423;  ar- 
senide, 422,  423,  425 ;  assay, 
305;  azure,  422;  black  oxide, 
233,  3oi.  304.  424;  blue,  423; 
blue  carbonate,  301,  305,  422; 
blue  malachite,  422;  carbon- 
ates, 301,  305  ;  cobalt  and  nickel 
sulphide,  423;  colors  in  cupel 
and  scorifier,  190;  element,  13; 
glance,  185,  232,  249,  298,  423; 
gray,  167,  186,  232,  249,  299, 
305,  420,  424;  green,  424;  green 
carbonate,  301,  305,  424;  indi- 
go, 423;  lead  and  antimony 
sulphide,  422,  425;  matte,  186; 
metal,  16;  metallic,  148;  metal- 
lurgy, 432 ;  minerals  in  the 
United  States,  422;  muriate, 
422;  native,  304,  421,424;  na- 
tive, assay,  306;  occurrence, 
304;  oxides,  301,  304;  oxides, 
assay,  301,  307;  oxy-chloride, 
422;  phosphate,  424;  purple, 
422;  pyrites,  185,  232,  249,  299, 
423;  pyritous,  423;  red  oxide,  \ 
304,  423;  silicate,  423;  spatu-  , 


las,  36;  sulph-arsenite,  423, 
424;  sulphate,  422,  423;  sul- 
phides or  sulphurets,  232,  298, 
305,  423;  sulphides,  assay,  307; 
tests  for,  410;  uranite,  424; 
variegated,  232,  422 ;  vitreous, 
232,  298,  423;  vitriol,  423; 
volumetric  analysis,  343. 

COPPERAS,  re-agent,  149. 

COPP'S  AMERICAN  MINING  CODE, 

435- 

CORBIN,  H.  H.,  reference  to,  177. 

"  CORNETS,"  394. 

CORN  STARCH,  reducing  power 
of,  134- 

"CORNUCOPIAS,"  lead,  391. 

CORNWALL'S  BLOW-PIPE  ANALY- 
SIS, 431. 

CORROSIVE  SUBLIMATE,  re-agent, 
148. 

"CORUSCATION,"  205. 

COTTA'S  TREATISE  ON  ORE  DE- 
POSITS, 430. 

COUNTERPOISING,  397. 

COVELLITE,  mineral,  299,  423. 

CREAM  OF  TARTAR,  re-agent,  128, 
133,  222;  reducing  power,  134, 
161. 

CRUCIBLE,  process,  171,  180,  181, 
217. 

CRUCIBLE  TONGS,  92. 

CRUCIBLES,  alumina,  103;  Batter- 
sea,  104-5;  black  lead  (graphite 
or  plumbago),  charcoal-lined, 
103;  clay,  104;  "Colorado," 
105;  French  clay  or  "Beau- 
fay,"  103,  104;  gold,  103; 


468 


INDEX. 


"Gramme,"       105;       Hessian, 

iron,  magnesia,  platinum,  103; 

porcelain,  103,  112;  quicklime, 

103;    round,    104;    sand,    104; 

silver,  104;  triangular,  104. 
CRUSHERS,  Alden,   Blake,    Fors- 

ter.   Lipsey,  24;   Bosworth,  27; 

Krom,  25. 
CUPEL,  color  tests,  190;  moulds, 

123;      rake,    98;     shovel,     98; 

tongs,  96. 

CUPELLATION,    183,   2OO. 

CUPELS,  directions  for  making, 
107. 

CUPREOUS,  bismuth,  422;  oxide, 
423;  sulphato-carbonate  of 
lead,  423,  425. 

CUPRIC  OXIDE,  mineral,  424. 

CUPRITE  (or  cuprous  oxide),  min- 
eral, 301,  304,  423. 

CUPS,  annealing,  no. 

CYANIDE  OF  POTASH,  properties, 
131;  re-agent,  128,  130,  146. 

CYCLOPEDIA,  Johnson's  New 
Universal,  428. 

CYLINDERS,  measuring,  114. 

D 

DANA,  Manual  of  Geology,  430; 
Manual  of  Mineralogy,  431; 
reference  to,  427;  System  of 
Mineralogy,  427,  430;  Text 
Book  of  Geology,  430. 

DARK  RED  SILVER  ORE,  168,  420. 

DAVIES,  D.  C.,  Treatises  on  Min- 
erals, 433. 


DAVYUM,  element,  14. 

DECHENITE,  mineral,  425. 

DECIPIUM,  element,  14. 

"  DECOMPOSED  iron  ore,"  233. 

DEFINITIONS,  of  analysis,  15;  of 
assaying,  15. 

DENDRITIC  SILVER,  419. 

DENVER  FIRE-CLAY  CRUCIBLES, 
105. 

DESCLOIZITE,  mineral,  425. 

DESULPHURIZING  ACTION,  of  bi- 
carbonate of  soda,  129;  of  car- 
bonate of  ammonia,  135;  of 
cyanide  of  potash,  131 ;  of  iron, 
141;  of  litharge,  140. 

DETERMINATION  OF,  moisture  in 
an  ore,  415;  oxidizing  power  of 
nitre,  153,  162;  of  ores,  251; 
reducing  powers  of  argol,  161; 
charcoal,  162;  cream  of  tartar, 
161;  ores,  242;  reducing  agents, 
153,  161;  sulphurets  in  an  ore, 
240;  sulphur  in  pyrites,  416. 

DI-CHROMATE,  p  o  T  A  s  s  I  c  ,  re- 
agent, 145. 

DICTIONARY  OF  CHEMISTRY, 
Watts',  428. 

DIDYMIUM,  element,  14. 

DIRECTIONS  FOR,  cupellation,  200; 
filtering,  336;  operating  Hos- 
kins'  furnace,  81;  sampling 
ores,  172;  setting  up  and  test- 
ing pulp  scales,  39;  special,  for 
bullion  balances,  54. 

DISHES,  ROASTING,  105. 

DISTILLED  WATER,  chlorine  in, 
142;  re-agent,  142. 


INDEX. 


469 


DIVIDERS,  31. 
DOMEYKITE,  mineral,  423. 
DOUGLAS  &  PRESCOTT'S  QUALI- 
TATIVE ANALYSIS,  429. 
"  DRESSING"  charges,  272. 
"  DRIVING,"  392. 
DRY  RE-AGENTS,  list  of,  128. 
DYSCRASITE,  mineral,  419. 


EGLESTON'S  WEIGHTS,  MEASURES, 
AND  COINS,  435,  449. 

EGLESTON'S  METALLURGY,  433. 

ELDERHORST'S  BLOW-PIPE  ANAL- 
YSIS, 431. 

ELECTRUM,  mineral,  417,  419. 

ELEMENTS,  lists  of,  13,  14. 

ELEMENTS  OF  CHEMISTRY.  MIL- 
LER'S, 428. 

ELIOT  AND  STORER'S  QUALITA- 
TIVE ANALYSIS,  429. 

EMBOLITE,  mineral.  419. 

ENAKGITE,  mineral,  421,  423. 

ENGINEERING  AND  MINING  JOUR- 
NAL, references  to,-i72,  350,405. 

ENGLISH  AND  FRENCH  WEIGHTS, 
equivalents  of,  449. 

EPSOM  SALTS,  re-agent,  149. 

ERBIUM,  element,  14. 

ERUBESCITE,  mineral,  232,  299, 
422. 

EUSTIS,  W.  E.  C.,  reference    to, 

334- 

"  EVERY-DAY"  ores,  185. 
EXPLANATION      of      assay      ton 

weights,  60. 


FAHLERZ,  232,  299. 

FAHLORE,  silver,  mineral,  169. 

"  FEATHERING,"  204,  407. 

FERRIC  SESQUIOXIDE,  152. 

FERROCYANIDE,  POTASSIC,  re- 
agent, 146. 

FERRO-TELLURITE,  mineral,  418, 
421. 

FERROUS  sulphate,  re-agent,  149; 
sulphide,  re-agent,  149. 

FIELDING,  F.  E.,  references  to, 
343,  370. 

FIGURES,  steel,  126. 

FILINGS,  IRON,  re-agent,  141. 

FILTERING,  directions  for,  336. 

FILTER  paper,  117;  stands,  126. 

"  FINENESS,"  383. 

FIRE  CLAY,  in  clay  lute,  152. 

"  FLASHING,"  205. 

FLASKS,  litre,  114,  115;  parting  or 
boiling,  113. 

FLETCHER'S  gas  furnaces,  68,  264, 

317. 

FLOORS,  MUFFLE,  103. 
FLOUR,  re-agent,  128,  133,  162, 

222. 

FLOUR  GOLD,  167,  223,  417. 

FLUORINE,  element,  13. 

FLUOR  SPAR,  mineral,  278. 

FLUXES,  acid,  225,  227;  basic,  225, 
227;  bi-carbonate  of  soda,  128, 
129;  black  flux  substitute,  128. 
133;  borax,  128,  131;  carbonate 
of  potash,  128,  130;  Chapman's 
crucible,  279;  cyanide  of  pot- 


INDEX. 


ash,  128,  130;    flour,    128,   133; 

glass,   137;    litharge,   129,   139; 

metallic,  138,  140,  neutral,  131; 

nitre,     129,     135;     sand,     137; 

scales  for,  37;    silica,  129,  137; 

Stone's  universal,  278. 
FLUXING  POTS,  104. 
FOIL,    lead,   re-agent,  138;    lead, 

silver  in,  138,  153,  160;  silver, 

re-agent,  141. 
FOLIATED    TELLURIUM,    mineral, 

417,  427. 

FORM  FOR  CERTIFICATE  OF  AS- 
SAY, 438. 

FORSTER  CRUSHER,  24. 
FOYE'S  MINERAL  TABLES,  431. 
FRAZER'S  MINERAL  TABLES,  431. 
FREE  GOLD,  167,  417;  assay  of  in 

ores,  329;  in  ores,  to  grind,  177. 
FREE   SILVER,  419;   assay   of    in 

ores,  329. 
"FREEZING,"  209. 
FREIESLEBENITE,    mineral,    419, 

426. 
FRENCH    CLAY    CRUCIBLES,    103, 

104. 
FRENCH  OR  METRIC  WEIGHTS,  59; 

equivalents  in  English  weights, 

449;  tables  of,  447. 
FRESENIUS'     QUALITATIVE     AND 

QUANTITATIVE  ANALYSIS,  429; 

reference  to,  414. 
FRYING  PAN,  123. 
FUEL,  metallurgy,  Percy,  432. 
"  FUGURATION,"  205. 
FUNNELS,  glass,  115;  separatory, 


FURNACES,  64;  apparatus  used  in, 
102;  Battersea,  84;  Brown's, 
86;  Fletcher's,  68;  gas,  group 
of,  67;  Hoskins',  78;  Judson's, 
85;  "  Monitor,"  70;  permanent, 
90;  portable,  83;  tools  for,  92; 
using  gaseous  fuel,  66;  using 
liquid  fuel,  77;  using  solid  fuel, 
S3- 


GADOLINIUM,  element,  14. 
GALENA  or  galenite,  167,  169,  187, 

232,   238.   249,    311,    418,   421, 

426;  crucible   charge  for,   303; 

iron  in  assay  of,  141,  313,  315, 

317;  methods  for,  312;  scorifi- 

cation  charge  for,  187. 
GALLIUM,  element,  14. 
GANGUES,    acid   and   basic,    225, 

227. 
GAS    FURNACES,     Fletcher's,    68; 

"  Monitor,"  70. 
GAS,  hydrogen  sulphide,  re-agent, 

149. 
GAUZE,  wire,  122. 

"GEM  PLATE,"   100. 

GENERAL  chemistry,  books  on, 
428;  charges  for  crucible  proc- 
ess, 276 ;  qualitative  and  quan- 
titative analysis,  books  on,  429; 
science,  books  on,  428. 

GEOCRONITE,  mineral,  421,  426. 

GEOLOGY,  books  on,  430. 

GERMANIUM,  element,  14. 

GLANCE,  copper,  185,  232,  249, 
298,423;  lead,  169;  silver,  168, 


INDEX. 


471 


232,  418;  silver-copper,  169, 
420,  424. 

GLASS,  and  porcelain  apparatus, 
in;  beakers,  114;  borax,  128, 
131;  borax,  preparation,  132; 
case  for  pulp  scales,  38;  flasks, 
114,  115;  funnels,  115;  magnify- 
ing, 125;  mortars,  116;  pi- 
pettes, 115;  re  agent,  137;  stir- 
ring rods,  115;  spatulas,  36. 

GLASSES,  watch  or  clock,  112. 

GLUCINUM,  element,  14. 

GLYCERINE,  for  sulphuretted  hy- 
drogen water,  151. 

GOLD,  amalgam,  417,  421;  and 
lead  telluride,  417;  argentifer- 
ous, 417,  419;  assaying  of,  170; 
assaying  of  free,  329;  bullion 
assay,  369;  chlorination  assay, 
364;  crucible,  103;  crucible 
process,  217;  element,  13;  flour, 
free,  leaf,  native,  nugget,  wire, 
167,  417;  in  silver  foil,  141; 
Lock's  work  on,  432;  metal,  16; 
minerals  in  United  States,  417; 
minerals  likely  to  carry,  418; 
multiplication  table,  443;  na- 
tive, 417,  421;  native,  assay, 
189;  occurrence,  167;  pan  test 
or  "panning,"  355;  residues, 
weighing  of,  183,  215;  tellu- 
ride, 417,  427;  tables  of  values 
of,  403,  444  ;  testing  of  silver 
foil  for,  141;  washing  pans,  126. 

"  GOLD  WEIGHTS,"  64,  382. 

GOLD  AND  SILVER,  and  lead  tellu- 
ride, 417,  426;  assaying,  167, 


170;  beads,  balances  for  weigh- 
ing, 44;  beads,  weighing  of, 
183,  209;  bullion,  assay  of,  369; 
calculations,  216  ;  crucible 
process,  217;  cupellation,  183, 
200;  inquartation,  183,  214; 
metallurgy,  books  on,  431; 
multiplication  table,  443;  oc- 
currence, 167;  ores,  charges 
for,  277-282  ;  parting,  210  ; 
preparation  of  charge,  183  ; 
preparation  of  sample,  171  ; 
residue,  weighing,  215;  roast- 
ing, 183,  185,  257,  259;  scorifi- 
cation  charges,  185;  scorifica- 
tion  process,  181;  table  of  val- 
ues. 403,  444;  tellurides,  417, 
419,  420. 

GRADUATED  APPARATUS,  114. 

GRAIN  WEIGHTS,  64. 

"GRAMME"  CRUCIBLES,  105. 

GRAMME  WEIGHTS,  59. 

GRANULATED  LEAD,  preparation, 
138;  re-agent,  129,  138;  test- 
ing for  silver,  138,  153,  158. 

"GRANULATION,"  381. 

GRAPHIC  TELLURIUM,  mineral, 
417,  420. 

GRAPHITE  CRUCIBLES,  103. 

GRAY,  antimony,  232,  249;  cop- 
per, 167,  186,  232,  249,  299,  420, 
424  ;  copper,  argentiferous,  169. 

GREEN,  carbonate  of  copper,  301, 
305,  424;  copper  ore,  424;  lead 
ore,  426;  malachite,  305,  424; 
mountain,  423,  424;  vitriol, 
149- 


472 


INDEX. 


GRINDER,  29. 

GRINDING  PLATE,  28;  Mr.  S.  A. 

Reed's,  30. 
GUM  ARABIC,  134. 
GUMMED  LABELS,  116. 

H 

HAMMERS,  118. 

HAND  SCALES,  43. 

HANKS,  H.  G.,  reference  to,  370, 

387- 
HANKS,   H.  G.,   Report  of  State 

Mineralogist  of  CaL,  431. 
HARD  COAL,  reducing  power  of, 

134- 

HARRISITE,  mineral,  299,  423. 
HART,  references  to,  351,  414. 
HART'S  VOLUMETRIC  ANALYSIS, 

430- 

HEAVY  SPAR,  mineral,  278. 

HELIUM,  element,  14. 

HEMATITE,  re-agent,  152;  min- 
eral, 296. 

HENRYITE,  mineral,  418,  421,  426. 

HESSIAN  CRUCIBLES,  103. 

HESSITE,  mineral,  418,  419,  421. 

HOLMIUM,  element,  14. 

HORN,  silver,  mineral,  168,  419; 
spatulas,  36;  spoons,  36. 

"  HORSE-FLESH"  ORE,  232,  299, 
422. 

HOSKINS*  ASSAY  FURNACE,   78. 

HYDRATE,  ammonic,  re-agent, 
144;  potassic,  re-agent,  146; 
sodic,  re-agent,  146. 

HYDRIC  NITRATE,  re-agent,  143. 


HYDROCHLORIC  ACID,  re-agent, 
147. 

HYDROGEN,  element,  13;  sulphide, 
149;  sulphide,  preparation  of 
as  re-agent,  150. 

HYDRO-POTASSIC-TARTRATE,  re- 
agent, 133. 

HYDRO -SODIC -CARBONATE,  re- 
agent, 129. 

HYDROXIDE,  CALCIC,  re-agent, 
147. 

HYPOSULPHITE  OF  SODIUM,  re- 
agent, 147. 


IDUNIUM,  element,  14. 
ILMENIUM,  element,  14. 
IMPLEMENTS    FOR    PULVERIZING, 

SAMPLING,  etc.,  20. 

IMPORTANCE  OF  AVERAGE  SAM- 
PLES, 172. 

IMPORTANT  SILVER  ORES,  168. 

INDIGO  COPPER,  mineral,  423. 

INDIUM,  element,  14. 

INGOT  MOULDS,  125. 

INQUARTATION,  183,  214. 

INTRODUCTION,  13. 

IODIC  SILVER  (iodide  of  silver,  io- 
dyrite),  i6q,  419. 

IODIDE  OF  POTASH,  re-agent,  147. 

IODINE,  element,  13. 

IRIDIUM,  element,  13. 

IRON,  and  copper  sulphide,  sul- 
phuret,  or  pyrites,  167,  185,  232, 
299,  305,  422,  423;  and  silver 
sulphide,  420;  brief  scheme  for, 


INDEX. 


473 


413;  colors  in  cupel  and  scori- 
fier,  191;  crucibles,  103;  desul- 
phurizing action,  141 ;  element, 
13;  filings,  141;  in  copper  ores, 
349,  350;  metal,  16;  metallic, 
148;  mortars,  20,  22;  nails,  141; 
oxide,  167,  187;  oxide,  crucible 
charges  for,  297,  298;  oxide, 
re-agent,  142;  pyrites,  crucible 
charges  for,  285,  289,  291,  292, 
293;  pyrites,  mineral,  231,  249, 
283;  pyrites,  re-agent,  142;  re- 
agent, 129,  141;  red  oxide,  152, 
233;  retorts,  127;  spatula,  36; 
sulphate,  149;  sulphide  or  sul- 
phuret,  re-agent,  149;  sulphu- 
rets,  ores,  186,  231,  232,  283; 
tests  for,  410;  wire,  141. 
IVORY  SPATULAS,  36. 


"JACK,  BLACK,"  231. 

JACKSON,  J.  C.,  reference  to,  92. 

JAMESONITE,  mineral,  426. 

JOHNSON'S  NEW  UNIVERSAL  CY- 
CLOPAEDIA, 428. 

JOSEITE,  mineral,  418,  421. 

JUDSON'S  cupel  tongs,  97;  fur- 
naces, 85;  scorification  tongs, 
95- 

K 

KERL'S  METALLURGY,  432;  Works 

on  Assaying;  434. 
KOBELLITE,  mineral,  426. 


KROM'S   LABORATORY   CRUSHER, 

25- 
KUNHARDT'S   PRACTICE   OF  ORE 

DRESSING,  433. 
KUSTEL,  references   to,  168,  365, 

367,  369;  Roasting  of  Gold  and 

Silver  Ores,  168,  432. 


LABELS,  gummed,  116. 

LABORATORY,  arrastre,  33;  ma- 
nipulation, books  on,  430;  mill- 
run,  351;  plan  of  assay,  437. 

LAMBORN'S  METALLURGY,  432. 

LAMPS,  122. 

LANARKITE,  mineral,  426. 

LANTHANUM,  element,  14. 

LAUNDRY  STARCH,  134. 

LEAD,  acetate,  141;  and  alumina 
phosphate,  427;  and  antimony 
sulphide,  425;  and  copper  chro- 
mate,  425,  427;  and  gold  tellu- 
ride,  417,  427;  and  silver,  anti- 
monial  sulphide  of,  419,  426; 
and  silver,  metallurgy,  432;  and 
zinc  vanadate,  425;  argentifer- 
ous ores,  169;  arsenate,  426; 
assay,  312;  bismuth  and  anti- 
mony sulphide,  426;  bismuth 
and  silver  sulphide,  418,  425 ; 
carbonate,  mineral,  170,  312, 
425;  carbonate,  re-agent,  141; 
carbonates,  assay,  320;  colors 
in  cupel  and  scorifier,  191;  cop- 
per and  antimony  sulphide,  422, 
425;  "cornucopias,"  391;  cu- 


474 


INDEX. 


preous-sulphato-carbonate,  425 ; 
element,  13;  foil,  re-agent,  138; 
foil,  silver  in,  138,  153,  160; 
glance,  169;  granulated,  prepa- 
ration, 138;  granulated,  re- 
agent, 129,  138;  granulated, 
silver  in,  139,  153,  158;  in  cop- 
per ores,  349,  350;  metal,  16; 
metallurgy,  432;  minerals,  425; 
molybdate,  427;  native,  427; 
ore,  green,  426;  ore,  white, 
312,  425;  ore,  yellow,  427;  ores, 
311;  ores,  argentiferous,  169; 
ores,  assay,  312;  ores,  occur- 
rence, 311;  oxides,  assay,  320; 
phosphate  of  alumina  and,  427; 
phosphate  and  chloride  of,  427; 
pyrites,  232,  302;  red  oxide, 
mineral,  233,  312;  red  oxide, 
426;  removal  from  litharge, 
139;  sheet,  silver  in,  138,  153, 
160;  silver  and  bismuth  sul- 
phide, 418,  420,  425,  427;  sil- 
ver and  gold  telluride,  417,  426; 
spar,  427;  sugar  of ,  141;  sulph- 
antimonite,  426;  sulph-arseno- 
antimonite,  426;  sulphate,  min- 
eral, 425;  sulphate-carbonate, 
423,  426;  sulphates,  assay,  312; 
sulphide  or  sulphuret, assay ,  312 ; 
sulphide,  or  sulphuret,  mineral, 
169,  232,  302,  311,  426;  sul- 
phide, iron  in  assay  of,  313, 
3I5»  317>  telluride,  425,  426; 
test  for,  411;  tungstate,  427; 
vanadate,  425;  vitriol,  425; 
white,  re-agent,  141;  yellow 


oxide,  mineral,  426;  yellow  ox- 
ide, re-agent,  139. 

LEADHILLITE,  mineral,  426. 

LEAF  gold,  167,  417;  silver,  419. 
i  LE  CONTE'S   ELEMENTS    OF   GE- 
OLOGY, 430. 

LEUCOPYRITES,  mineral,  421. 

LIBBER'S  ASSAYER'S  GUIDE,  434. 

LIGHT  RED  SILVER  ORE,  168,  419. 

LIME,  in  copper  ores,  349;  sul- 
phate of,  424. 

LIME  water,  re-agent,  147. 

LIMONITE,  mineral,  296. 

LIGNITE,  mineral,  418,  421. 

LlPSEY  CRUSHER,    24. 

LISTS  AND  REFERENCES,   417. 

LISTS,  copper  minerals,  422;  dry 
re-agents  for  assaying,  128;  ele- 
ments, 13,  14;  gold  minerals, 
417;  lead  minerals,  425;  min- 
erals carrying  gold,  418;  min- 
erals carrying  silver,  421;  re- 
agents' for  analysis,  144;  silver 
minerals,  418;  useful  books,  428; 
wet  re-agents  for  assaying,  142. 

LITHARGE,  properties,  140;  re- 
agent, 129,  139,  222;  to  free 
from  red  oxide,  139;  silver  in, 
140,  153,  154. 

LITHIUM,  element,  13. 

LITRE  FLASKS,  114. 

LOCK'S  WORK  ON  GOLD,  432. 

Low,  A.  H.,  reference  to,  293. 

LUCKOW  method  of  copper  anal 
ysis,  333. 

LUNAR  CAUSTIC,  re-agent,  148. 

LUTE,  CLAY,  152. 


INDEX. 


475 


M 

MAGNESIA,  crucibles,  103;  in  cop- 
per ores,  349. 

MAGNESIUM,  element,  13;  sul- 
phate, re-agent,  149. 

MAGNET,  125. 

MAGNETIC  IRON  PYRITES,  etc., 
231,  283. 

MAGNIFYING  GLASS,  125. 

MAGNOLITE,  mineral,  418,  421. 

MAKIN'S  MANUAL  OF  METAL- 
LURGY, 433. 

MALACHITE,  301,  424;  blue,  422; 
green,  305,  424. 

MANGANBLENDE,  231,  238,  249. 

MANGANESE,  black  or  di-oxide, 
145,  233;  brief  scheme  for,  413; 
colors  in  cupel  and  scorifier, 
192;  element, 13;  in  copper  ores, 
348;  sulphuret,23i;  test  for,  411. 

MANIPULATION,  LABORATORY. 
books  on,  430. 

MARCASITE,  283. 

MASSICOT,  mineral,  426. 

MATRASSES,  113. 

MATTE,  COPPER,  186. 

MATTES,  275. 

MEASURING  CYLINDERS,  114. 

MELACONITE,  mineral,  233,  301, 
304,  418,  421,.  424. 

MERCURY,  chloride,  148;  ele- 
ment, 13;  metallic,  148;  nat- 
ive, 421;  re-agent,  148;  sul- 
phuret,  232;  with  gold,  417. 

METALLIC  copper,  iron,  mercury, 
zinc,  148;  scales,  177,  329. 


METALLURGY  AND  MINING,  books 
on,  432. 

METHODS,  assay  for  copper  ox- 
ides and  carbonates,  307;  assay 
for  copper  sulphides,  307;  as- 
say for  galena,  312;  assay  for 
iron  pyrites,  284;  assay  for 
lead  oxides  and  carbonates, 
320;  assay  for  native  copper, 
306;  of  assaying,  180;  of  cop- 
per analysis,  333 ;  of  crucible 
assays,  264;  special,  327. 

METRIC  SYSTEM,  books  on,  435. 

MEO-RIC  WEIGHTS,  59;  equivalents 
in  English,  449;  tables  of,  447. 

MIARGYRITE,  mineral,  168,  419. 

MILL,  coffee,  133;  run,  labora- 
tory, 351. 

MILLER'S  ELEMENTS  OF  CHEMIS- 
TRY, 428. 

MIMETITE,  mineral,  426. 

"  MINERAL,"  232. 

MINERALOGY,  books  on,  430. 

MINERALS,  assaying  of,  in  an  ore, 
327;  copper,  422;  gold,  417; 
lead,  425;  likely  to  carry  gold, 
418;  likely  to  carry  silver,  421; 
silver,  418. 

MINERS'  gold  washing  pans,  126. 

MINING  LAW,  books  on,  435. 

MINIUM,  mineral,  233   312,  426. 

MISCELLANEOUS,  apparatus,  116; 
materials,  152. 

MISPICKEL,  mineral,  231. 

MITCHELL,  references  to,  78,  90, 
108,  139,  140,  204,  277,  310, 
323,  3Qi. 


476 


INDEX. 


MITCHELL'S  MANUAL  OF  PRAC- 
TICAL ASSAYING,  435. 

MOISTURE  in  ores,  determination 
of,  415- 

MOLYBDATE  OF  LEAD,  mineral, 
427. 

MOLYBDENUM,  element,  13. 

"  MONITOR  "  gas  furnace,  70. 

MORFIT'S  CHEMICAL  MANIPULA- 
TION, 430. 

MORTAR,  amalgamation,  33. 

MORTARS  AND  PESTLES,  glass, 
116;  iron,  20,  22;  porcelain, 
116;  spring  attachment  for,  21. 

MOSANDRIUM,  element,  15. 

MOULDS,  cupel,  123;  ingot,  125; 
scorifier,  scorification,  or  slag, 
99. 

MOUNTAIN  blue,  422,  423;  green, 

423,  424- 
MUFFLE,  floors,  103;  hoe  or  rake, 

98,  101;    scraper,   101;    shovel, 

98,  101. 
MUFFLES,  102. 

MULLER,   29. 

MULLERITE,    mineral,    417,    421, 

426. 
MULTIPLICATION    TABLE    FOR 

GOLD  AND  SILVER,  443. 

MUNDIC,  231,   283. 

MURIATE  OF  BARYTA,  146;  of  cop- 
per, 422;  of  silver,  419. 
MURIATIC  ACID,  147. 

N 

NAGYAGITE,  mineral,  417,  421, 
427. 


NAILS,  iron,  re-agent,  141. 

NATIVE,  antimony,  421 ;  arsenic, 
418,  421;  bismuth,  418,  421; 
copper,  304,  421,  424;  copper, 
assay,  306;  gold,  417,  421;  gold, 
assay  189;  lead,  427;  mercury, 
421;  silver,  418,  419;  silver  as- 
say, 189;  tellurium,  418,  421. 

NEEDLE  ORE,  mineral,  422. 

NEPTUNIUM,  element,  15. 

NICKEL  cobalt  and  copper,  sul- 
phide, 423;  cupel  color,  193; 
element,  13;  in  copper  ores, 
347;  metal,  16;  scorifier  color, 
192. 

NITRATE  OF  SILVER  (or  argentic), 
re-agent,  143,  148. 

NITRE,  oxidizing  power,  135,  153, 
162;  re-agent,  129,  135,  222. 

NITRIC,  acid,  preparation  of  vari- 
ous strengths,  211;  re-agent, 
143,  148;  to  free  from  chlorine, 

143- 

NITROGEN,  element,  13. 
NIXON,     M.    G.,     Amalgamation 

Assay,  351. 
NORTH'S    PRACTICAL  ASSAYING, 

435- 

NORWEGIUM,  element,  14. 
NOTE-BOOKS,  116. 
NOTES  ON  SETTING  UP  the  Oert- 

ling  Balance,  48. 
NUGGET  GOLD,  167,  417. 


OCHRE,  PLUMBIC,  426. 
OCCURRENCE    OF    ORES,    copper, 


INDEX. 


477 


304;  gold,  167;  gold  and  silver, 
167;  lead,  311;  silver,  167. 

OERTLING'S  BULLION  BALANCE, 
48 ;  notes  on  setting  up,  48. 

OIL  CLOTH  for  sampling,  117. 

OIL  OF  VITRIOL,  re-agent,  151. 

OLDBERG,  O.,  Weights,  Measures, 
and  Specific  Gravity,  435. 

ORDER  OF  WORK,  in  assaying, 
171;  in  scorification  process, 
183. 

"ORDINARY  ORES,"  281,  282. 

ORE,  antimonial  silver,  168;  ar- 
gentiferous gray  copper,  169; 
arsenical  silver,  168,  419;  as- 
saying of  minerals  in,  327; 
azure  copper,  422;  brittle  sil- 
ver, 168;  dark  red  silver,  168, 
420;  gray  copper,  299,  420, 
424;  green  copper,  424;  green 
lead,  426;  "horse  flesh,"  422; 
light  red  silver,  168,  419;  nee- 
dle, 422;  purple  copper,  422; 
"  tile,"  423;  variegated  copper, 
422;  white  lead,  312,  425;  yel- 
low lead,  427. 

ORES,  analysis  of  copper,  333; 
argentiferous  lead,  169;  arsen- 
ical and  antimonial,  185 ;  blende, 
188;  "carbonate."  167,  187; 
"chloride,"  169,  187;  chlorina- 
tion  assay  of  gold,  364;  con- 
taining free  gold  or  silver,  as- 
saying of,  329;  copper,  304, 
422;  copper,  assay,  305;  copper 
glance  or  pyrites,  185,  298; 
copper  matte,  186;  copper,  oc- 


currence, 304;  determination  of 
moisture  in,  415;  directions  for 
sampling,  174;  "every-day," 
186;  galena,  187;  gold,  167; 
gold,  assay,  170;  gold,  occur- 
rence, 167;  gold  and  silver, 
167;  gold  and  silver,  assay,  170; 
gold  and  silver,  charges  for, 
277,  282;  gold  and  silver,  oc- 
currence, 167;  gray  copper 
ore,  187;  important  silver,  168; 
lead,  311;  lead,  assay,  312; 
lead,  occurrence,  311;  native 
gold  and  silver,  189;  oxide  of 
iron,  187;  oxidizing  powers, 
228;  pulverizing,  176;  reducing 
powers  of,  228;  silver,  418;  sil- 
ver, assay,  170;  silver,  occur- 
rence, 167;  sulphurets  of  iron, 
186;  tellurides,  188;  volumetric 
analysis  of  copper,  343. 

OSMIUM,  element,  14. 

OUTFIT,  assaying,  439 ;  blow-pipe, 
441. 

OVERMAN'S  ASSAYING,  435. 

OXIDE,  antimony,  420;  copper, 
304;  copper,  black,  232,  301, 
304,  424;  copper,  red,  301,  304, 
423;  cupric,  424;  cuprous,  423 ; 
iron,  167,  187;  iron,  crucible 
charges  for,  297,  298;  iron,  re- 
agent, 142;  iron,  red,  152,  233; 
lead,  red,  mineral,  233,  312, 
426;  lead,  red,  to  remove  from 
litharge,  139;  lead,  yellow, 
mineral,  426;  lead,  yellow,  re- 
agent, 139;  manganese,  black, 


478 


INDEX. 


re-agent,  145;  manganese, 
black,  mineral,  233;  uranium, 
424. 

OXIDES,  copper,  assay,  307;  lead, 
assay,  320. 

OXIDIZING,  action  of  bi-carbonate 
of  soda,  129;  action  of  nitre, 
135;  action  of  ores,  228;  power 
of  nitre,  153,  162. 

OXY-CHLORIDE  OF  COPPER,  min- 
eral, 422. 

OXYGEN,  element,  13. 


PALLADIUM,  element,  13. 

PAN  TEST  on  "panning"  for 
gold,  355- 

PANS,  frying,  123;  miners'  gold- 
washing,  126;  zinc  sifting,  35. 

PAPERS,  black  glazed,  blotting, 
brown  or  manilla,  filter,  tissue, 
117. 

"  PARTING,"  183,  210. 

PARTING-FLASKS,  113. 

"  PEPPER  CARBONS,"  394. 

PERCY'S  METALLURGY,  432. 

PERMANENT  FURNACES,  90. 

PETZITE,  mineral,  417,  419,  421. 

PHILIPPIUM,  element,  15. 

PHILLIPS'  ASSAYERS'  COMPANION, 

435- 

PHILLIPS'  METALLURGY,  etc.,  433. 
PHOSPHATE,  and  chloride  of  lead, 

427;  of  alumina  and  lead,  427; 

of  copper,  424;  of  uranium  and 

copper,  424. 


PHOSPHORUS,  element,  14. 

PINCERS,  118. 

PIPETTES,  115. 

PLAN  OF  ASSAY  LABORATORY,  437. 

PLATE,  annealing,  no;  gem,  100; 
pouring,  99;  pulverizing  or  rub- 
bing, 28. 

PLATINUM,  crucibles,  103;  dish, 
337;  element,  14;  metal,  16; 
spatulas,  36;  vessels,  127. 

PLATTNER,  reference  to,  91,  44. 

PLATTNER'S  BLOW-PIPE  ANALY- 
SIS, 431. 

PLUMBAGO  crucibles,  103. 

PLUMBIC,  acetate,  re-agent,  141; 
carbonate,  re-agent,  141;  mon- 
oxide, re-agent,  139;  ochre, 
426. 

PLUMBOGUMMITE,  mineral,  427. 

PLYMPTON'S  BLOW-PIPE  DETER- 
MINATION, 431. 

"  POINTS,"  396. 

POKERS,  101. 

POLYBASITE,  mineral,  168,  419. 

POMEROY'S     MINING     MANUAL, 

433- 

PORCELAIN,  and  glass  apparatus, 
in;  casserole,  115;  crucibles 
or  capsules,  103,  112;  mortars, 
116;  spatulas,  36. 

PORTABLE  FURNACES,  83. 

POTASH,  bi-carbonate,  222;  car- 
bonate, 128,  130,  222;  caustic, 
or  hydrate,  146;  cyanide,  130, 
146;  bi-  or  di-chromate,  145 ; 
bi-tartrate,  128,  133,  161;  fer- 
rocyanide,  146;  iodide,  147; 


INDEX. 


479 


nitrate,  135,  153,  162;  sulpho- 
cyanide,  149;  yellow  prussiate, 
147. 

POTASSIUM,  element.  14. 

POTS,  FLUXING,  104. 

POURING  PLATES,  99. 

PRECIPITATED    SILICA,    re-agent, 

137- 

PREFACES,  5,  7. 

PRELIMINARY  CHARGES,  to  deter- 
mine oxidizing  power,  251;  re- 
ducing power,  242. 

PREPARATION  OF,  borax  glass,  132; 
charge  in  crucible  process,  267; 
charge  in  scorification  process, 
183;  granulated  lead,  138;  sam- 
ples, 171;  various  strengths  of 
nitric  acid,  211. 

PROCESS,  crucible,  171,  180,  181, 
217;  scorification,  171,  180, 
181. 

PROOF  CENTRES,  388. 

PROTO-CHLORIDE  OF  TIN,  re- 
agent, 149. 

PROUSTITE,  mineral,  419. 

PRUSSIATE    OF   POTASH,    yellow, 

147- 

PSEUDOMALACHITE,  mineral,  424. 

PULPS,  scales  for,  37;  setting  up 
and  testing,  directions  for,  39. 

PULVERIZER,  29;  Richards,  33. 

PULVERIZING  OF  ORES,  176;  sam- 
pling, etc.,  implements  for,  20; 
plate  and  rubbers,  28;  manner 
of  using,  178. 

PUNCH,  bullion,  126. 

PURPLE  COPPER  ORE,  299,  422. 


PYRARGYRITE,  mineral,  420. 

PYRITE,  mineral,  231,  283,  418, 
421. 

PYRITES,  231,  238,  249,  283;  ar- 
gentiferous, 170;  arsenical  iron, 
231,  235;  copper,  185,  249,  299, 
423;  crucible  charges  for,  285, 
289,  291,  292,  293;  determina- 
tion of  sulphur  in,  416;  iron 
and  copper,  167,  299;  iron,  re- 
agent, 142;  magnetic  iron,  231; 
of  lead,  232,  302. 

PYROLUSITE,  mineral,  233. 

PYROMORPHITE,  mineral,  427. 

PYRRHOTITE,  mineral,  231,  238, 
283. 


QUALITATIVE  ANALYSIS,  Douglas 
and  Prescott's,  429;  Eliot  and 
Storer's,  429;  Fresenius',  429; 
general,  books  on,  429. 

QUALITATIVE  TESTS,  408;  car- 
bonates, 408;  copper,  410; 
iron,  410;  lead,  411;  manga- 
nese, 411;  silver,  411;  sul- 
phates, 409;  sulphides,  409; 
tellurides,  409. 

QUANTITATIVE  ANALYSIS,  Cairns', 
429;  Classen's,  429;  Fresenius', 
429;  general,  books  on,  429; 
Rammelsberg's,  429;  special, 
books  on,  429;  Wohler's,  429. 

QUICKLIME  CRUCIBLES,  103. 

QUICKSILVER,  148. 


480 


INDEX. 


R 


RAKE,  cupel,  98. 

RAMMELSBERG'S  QUANTITATIVE 
ANALYSIS,  429. 

RANDALL'S  QUARTZ  OPERATOR'S 
HAND  BOOK,  433. 

RE-AGENTS,  dry,  for  assaying, 
128;  for  analysis,  144;  bottles 
for,  in;  in  scorification  pro- 
cess, 182;  testing  of,  153;  wet, 
for  assaying,  142. 

REALGAR,  mineral,  421, 

RED  OXIDE  OF  COPPER,  301,  304, 
423;  iron,  152,  233,  297;  lead, 
mineral,  233,  312,  426;  lead, 
removal  of,  from  litharge,  139. 

REDUCING  POWER  OF,  argol,  char- 
coal, coke,  corn  starch,  cream 
of  tartar,  gum  arabic,  hard 
coal,  laundr^tstarch,  134;  ores, 
228,  242,  251;  reducing  agents, 
134,  153,  161;  soft  coal,  wheat 
flour,  white  sugar,  134. 

REED,  S.  A.,  reference  to,  30,  364. 

REFERENCE  BOOKS  ON  CHEMIS- 
TRY, 428. 

REFERENCES  AND  LISTS,  417. 

REPORT  ON  COLORADO  MINERALS, 
427. 

REPORT,  Fourth  Annual,  for  Cal- 
ifornia, 370. 

RESIDUES,  gold,  weighing  of,  183, 

215- 

RETORTING  in  scorifiers,  354. 
RETORTS,  iron,  127. 
RHODIUM,  element,  14. 


RICHARDS'  PULVERIZER  or  labor- 
atory arrastre,  33. 
RICKETTS'  NOTES  ON  ASSAYING, 

435- 

RING  STAND,  121. 

ROASTING,  carbonate  of  ammonia 
used  in,  135,  263;  charcoal 
used  in, 259;  dishes,  105;  of  ores 
in  crucible  process,  257,  259; 
of  ores  in  scorification  process, 
183,  185;  silica  used  in,  259. 

ROCKER,  29. 

RODS,  glass  stirring,  115. 

ROLLS,  125. 

ROSCOE  and  Shorlemmer's  Chem- 
istry, 428 ;  Elementary  Chem- 
istry, 429. 

Ross,  W.  A.,  books  on  blow-pipe 
analysis,  432. 

ROUND  CRUCIBLES,  104. 

RUBBER,  iron,  29;  sheet  or  cloth, 
117. 

RUBBING  PLATE,  28. 

RUBIDIUM,  element,  14. 

RUBY  SILVER,  mineral,  168,  419, 
420. 

RUDDLE,  152. 

RUNNING  crucibles  in  fire,  273. 

RUTHENIUM,  element,  14. 

RUTLEY'S  STUDY  OF  ROCKS,  430. 


SALT,    COMMON,    re-agent,     129, 

135. 

SALTPETRE,  re-agent,  135. 
SALTS,    Epsom,    re-agent,    149; 

tin,  re-agent,  149. 


INDEX. 


481 


SAMARIUM,  element,  14. 

SAMPLE,  bottles,  in;  boxes,  117, 
172;  preparation  of,  171;  shov- 
els, 31, 

SAMPLERS,  31. 

SAMPLES,  to  obtain  average,  172. 

SAMPLING,  of  base  bullion,  406; 
implements  for,  20;  systematic, 

179- 

SAND,  baths,  122;  crucibles,  103, 
104;  in  accidents  to  muffles,  198; 
re-agent,  137. 

SCALES,  and  balances,  36;  hand, 
43;  pulps  and  fluxes,  37;  set- 
ting up  and  testing  pulp,  direc- 
tions for,  39. 

SCALES,  metallic,  177,  329. 

SCANDIUM,  element,  14. 

SCHAPBACHITE,  mineral,  420,  427. 

SCHEME    FOR    SILICA,  IRON,  AND 

MANGANESE,  413. 

SCHIRMERITE,  mineral,  420,  427. 
SCIENCE,  GENERAL,  books  on,  428. 
SCISSORS,  125. 

SCORIFICATION  PROCESS,  171,  l8o, 

181;  borax  glass  in,  182;  but- 
tons from,  196;  calculations, 
183,  216;  charges,  185;  cupel- 
lation,  183,  200;  granulated 
lead  in,  182;  inquartation,  183, 
214;  order  of  work,  183;  part- 
ing, 183,  210;  preparation  of 
charge,  183;  re-agents  used 
for,  182;  roasting  of  ores  in, 
183,  185;  scorification,  183, 
194;  scorifiers  from,  198;  silica 
in,  182,  199;  slag  from,  198; 


theory  of,  182;  weighing  gold 
and  silver  bead,  209;  weighing 
gold  residues,  216. 

SCORIFIER,  color  tests,  190; 
moulds,  99;  tongs,  94. 

SCORIFIERS,  106;  "  retorting"  in, 
354- 

SCRAPER,  MUFFLE,  101. 

SELENIUM,  element,  14. 

SEPARATORY  FUNNEL,  115. 

SESQUIOXIDE,  FERRIC,  re-agent, 
152- 

SETTING  UP  and  testing  pulp 
scales,  directions  for,  39. 

SETTING  UP  the  Oertling  balance, 
notes  on,  48. 

SHEARS,  125. 

SHEET  lead,  re-agent,  129,  138; 
testing  for  silver,  138,  153,  160; 
rubber,  for  sampling,  117. 

SHOVELS,  cupel,  98;  sample,  31. 

SIEVES,  34. 

SIFTING  OF  ORES,  176;  pans,  35. 

SILICA,  acid  flux,  137,  228;  brief 
scheme  for,  413;  in  scorifica- 
tion process,  186,  187,  199; 
precipitated,  137;  re-agent,  129, 
137,  222. 

SILICATE  OF  COPPER,  mineral, 
302,  423. 

SILICIC  DI-OXIDE,  re-agent,  137. 

SILICON,  element,  14. 

SILVER,  and  antimony  sulphide, 
168,  419,  420;  and  copper  sul- 
phide, 169,  420,  424;  and  gold, 
beads,  weighing  of,  183,  209; 
and  gold,  metallurgy,  432;  and 


482 


INDEX. 


gold,  multiplication  table,  443; 
and  gold  ores,  assaying,  170; 
and  gold  ores,  charges,  277, 
282;  and  gold  telluride,  417, 
419;  and  gold  values,  table  of, 
403,  444;  and  iron  sulphide,  420, 
and  lead,  antimonial  sulphide 
of,  419,  426;  and  lead,  metal- 
lurgy, 432 ;  antimonial,  419,  420; 
antimony  and  arsenic  sulphide, 
168,  419,  420;  arsenical,  419; 
assay,  170;  assaying  of  ores 
containing  free,  329;  bismuth, 
420;  bismuth  and  lead  sulphide, 
418,  420,  425,  427;  black,  420; 
brittle,  168,  420;  bromic  or 
bromide  of,  169,  418;  bullion, 
assay  of,  369;  chloride,  169, 
419;  chlorination,  test  for,  367; 
chloro-bromide,  419;  copper 
glance,  169,  420  424;  crucible, 
104;  dark  red,  168,  42.0;  den- 
dritic, 419;  element,  14;  fah- 
lore,  169;  foil,  gold  in,  141; 
foil,  re-agent,  141;  free,  419; 
glance,  168,  232,  418;  gold  and 
lead  telluride,  417,  426;  horn, 
168,  419;  in  copper  ores,  348, 
350;  in  granulated  lead,  139, 
153,  158;  in  lead  foil,  138,  153, 
160;  in  litharge,  140,  153,  154; 
iodic  or  iodide  of,  169,  419; 
leaf,  419;  lead  and  bismuth 
sulphide,  418,  420;  light  red, 
168,  419;  metal,  16;  metallur- 
gy, 432;  minerals  carrying,  421; 
minerals  in  United  States,  418  ; 


muriate,  419;  native,  418,  419; 
native,  assay,  189;  nitrate,  re- 
agent, 143,  148 ;  ores,  168 ; 
ores,  assaying,  170;  ores,  im- 
portant, 168;  ores,  occurrence, 
167;  ruby,  168,  419,  420;  spat- 
ulas, 36 ;  sulphide  or  sulphu- 
ret,  168,  232,  418;  telluric  or 
telluride,  419;  tests  for,  411; 

•  testing  of  granulated  lead 
for,  158;  testing  of  litharge 
for,  154;  testing  of  sheet  lead 
for,  160;  vitreous,  418;  wire, 
419. 

SILVERSMITH'S  HAND-BOOK  FOR 
ASSAYERS,  435. 

SLAG  from  scorification  process, 
198;  moulds,  99. 

SMALTITE,  mineral,  421. 

SMITH,  J.  A.,  Report  on  Colorado 
Minerals,  427. 

SODA,  bi-carbonate  of,  128,  129, 
222;  carbonate  of,  re-agent, 
145;  caustic  or  hydrate,  146. 

SODIC,  bi-borate,  re-agent,  131; 
carbonate,  145,  222;  chloride, 
135;  hyposulphite  or  thiosul- 
phate,  147. 

SODIUM,  element,  14. 

SOFT  COAL,    reducing  power  of, 

134- 

SPAR,  calc,  fluor,  heavy,  278;  yel- 
low lead,  427. 

SPATULAS,  35. 

SPECIAL,  charges  for  crucible  proc- 
ess, 282;  directions  for  bullion 
balances,  54;  methods,  327; 


INDEX. 


483 


quantitative  analysis,  books  on, 

429. 
SPHALERITE,    mineral,  231,  418, 

421. 

"SPITTING,"  207. 
SPOONS,  HORN,  36. 
SPRING   attachment   for  mortars 

and  pestles,  21. 
"SPROUTING,"  207. 
STAND,  burette,   127;  filter,   126; 

ring,  121. 
STANNOUS    CHLORIDE,    re-agent, 

149. 
STARCHES,   reducing   powers   of, 

134,  162. 
STEEL,  alphabets  and  figures,  126; 

spatulas,  36. 

STEPHANITE,  mineral,  168,  420. 
STERNBERGITE,  mineral,  420. 
STETEFELDITE,  mineral,  169,  420. 
STIBNITE,  232,  238. 
STIRRING  RODS,  glass,  115;  wire, 

261. 

STOLTZITE,  mineral,  427. 
STONE'S  universal  flux,  278. 
STOVES,  122. 
STROMEYERITE,  mineral,  169,  299, 

420,  424. 

STRONTIUM,  element,  14. 
SUBLIMATE,  corrosive,    re-agent, 

148. 
SUBSTITUTE,     black     flux,     128, 

133. 

SUGAR,    of    lead,    re-agent,    141; 
white,  134,  162. 

SULPH-ANTIMONITE        OF        LEAD, 

mineral,  426. 


SULPH-ARSENITE  OF  COPPER,  min- 
eral, 423,  424. 

SULPH-ARSENO-ANTIMONITE         OF 

LEAD,  mineral,  426. 
SULPHATES,     copper,    422,    423; 
iron,     149;     lead,     425;     lime, 
424;  magnesium,  149;  test  for, 
409. 

SULPHATO-CARBONATE,      of     lead, 

423,  426. 

SULPHIDES  or  SULPHURETS,  ac- 
tions of  and  upon,  249;  anti- 
mony, 232;  auriferous-,  167; 
bismuth,  silver,  and  lead,  418, 
420,  425,  427;  cobalt,  nickel, 
and  copper,  423;  copper,  232, 
298,  305,  423;  copper  and  iron, 

167,  232,   299,   305,    422,    423; 
copper     and     antimony,    232; 
copper,    lead,    and    antimony, 
422,  425;    determination  of   in 
an  ore,  240;  ferrous  or  iron  re- 
agent, 149;  iron,  186,  231,  283; 
iron  and  arsenic,  231 ;  iron  and 
copper,  167,  185,  232,  299,  305; 
lead,    169,   232,   302,  311,   426; 
lead  and  antimony,  425;  lead, 
bismuth,    and   antimony,  426; 
manganese,  231 ;    roasting  of, 
238;  silver,  168,  232,  418;  silver 
and  antimony,   168,   419,    420; 
silver  and  copper,  169  420,  424; 
silver  and  iron,  420;  silver  and 
lead,  antimonial,  419,  426;  sil- 
ver,   antimony,    and     arsenic, 

168,  419,  420;    tests   for,    234, 
235.  236,409:  zinc,  170,  231. 


484 


SULPHOCYANIDE     OF     POTASSIUM, 

re-agent,  149. 

SULPHUR,  element,  14;  determin- 
ation of,  in  pyrites,  416;  re- 
agent, 129,  142,  222;  vapors, 
colors  of, 

SULPHURETTED  HYDROGEN,  prep- 
aration, 150. 

SULPHURIC  ACID,  re-agent,  151. 

"  SURCHARGE,"  396. 

SUTTON,  references  to.  351,  414, 

415. 
SUTTON'S  VOLUMETRIC  ANALYSIS, 

430. 

"SWEET"  ORES,  261. 
SYLVANITE,    mineral,    417,    420, 

421. 
SYSTEMATIC   SAMPLING    of  ores, 

179. 


TABLES,  apothecaries'  weights, 
446;  assay  ton  weights  in 
grammes,  grains,  etc.,  450; 
avoirdupois  to  troy  weights, 
399;  avoirdupois  weights,  445; 
equivalents  of  English  and 
French  weights,  449;  French 
or  metric  weights,  447;  multi- 
plication for  gold  and  silver, 
443;  reducing  powers  of  reduc- 
ing agents,  134;  sulphurets, 
238,  249;  troy,  401,  446;  troy 
to  avoirdupois  weights,  401; 
values  of  gold  and  silver,  403, 
444;  weights,  443. 

TANTALUM,  element,  14. 


TARTAR,  cream  of,  re-agent,  128, 
133;  reducing  power,  161. 

TARTARIC  ACID,  re-agent,  151. 

TECHNOLOGY,  CHEMICAL,  WAG- 
NER'S, 428. 

TELLURIC  SILVER,  mineral,  419. 

TELLURIDES,  417;  by  scorification 
process,  188;  gold,  417;  gold 
and  lead,  417,  427;  gold  and 
'  silver,  417,  419,  420;  gold,  sil- 
ver, and  lead,  417,  426;  lead, 
425,  426;  silver,  417,  419;  test 
for,  409. 

TELLURITE,  mineral,  418,  421. 

TELLURIUM,  black,  417,  427;  col- 
ors in  cupel  and  scorifier,  193 ; 
element,  14;  foliated,  417,  427; 
graphic,  417,  420;  native,  418, 
421;  ores,  167;  with  gold,  417; 
yellow,  417,  420. 

TELLURPYRITE,  mineral,  418,421. 
I  TENNANTITE,  mineral,  299,  424. 

TENORITE,  mineral,. 233,  301. 

TERBIUM,  element,  15. 

TESTING  OF,  distilled  water  for 
chlorine,  142;  granulated  lead 
for  silver,  158;  litharge  for  sil- 
ver, 154;  pulp  scales,  directions 
for,  39;  re-agents,  153;  sheet 
lead  for  silver,  160;  silver  foil 
for  gold,  141. 

TESTS,  chlorination  for  silver, 
367 ;  cupel  and  scorifier  color, 
190,  194;  qualitative  for  car- 
bonates, copper,  iron,  lead, 
manganese,  silver,  sulphates, 
sulphides,  tellurides,  408- 


IfiDEX. 


485 


413;  for  sulphurets,  234,  235, 
236. 

TEST  TUBES,  113. 

TETRAUYMITE,  mineral,  418,  421. 

TETRAHEDRITE,  mineral,  232, 
238,  299,  305,  418,  420,  424. 

TEXT-BOOKS  on  theoretical  chem- 
istry, 428. 

THALLIUM,  element,  14. 

THEORY  OF,  crucible  process,  219; 
scorification  process,  182. 

THIOSULPHATE,  sodic,  re-agent, 
147. 

THORIUM,  element,  14. 

THULIUM,  element,  15. 

"  TILE-ORE,"  423. 

TIN,  element,  14;  metal,  16;  pro- 
to-chloride,  or  "tin  salts,"  re- 
agent, 149. 

TISSUE  PAPER,  117. 

TITANIUM,  element,  14. 

TONGS,  crucible,  92;  cupel,  96; 
scorifier,  94. 

TOOLS,   FURNACE,  92. 

TORBERNITE,  mineral,  424. 
TORREY   AND    EATON,    reference 

to,  350. 
TREATISE  ON,  Chemistry,  Roscoe 

and    Schorlemmer's,    428 ;    ore 

deposits,  Cotta's,  430. 
TRIANGLE,  WIRE,  121. 
TRIANGULAR  CRUCIBLES,  104. 
TRIPLE   SULPHURET   OF    COPPER, 

LEAD,  AND  ANTIMONY,  422,  425. 
TRIPLETT'S  How  TO  ASSAY,  435. 
TROEMNER'S  bullion  balances,  44, 

45,  46,  47,  48;  pulp  scales,  38. 


TROY  WEIGHTS,  tables  of,  401, 
446;  to  avoirdupois,  401. 

TUBES,  TEST,  113. 

TUNGSTATE  OF  LEAD,  mineral, 
427. 

TUNGSTEN,  element,  14. 

u 

UNITED  STATES,  minerals  found 
in;  copper,  422;  gold,  417; 
lead,  425;  silver,  418. 

UNIVERSAL  FLUX,  Stone's,  278. 

URANIUM,  and  copper,  phosphate, 
424;  colors  in  cupel  and  scor- 
ifier, 193;  element,  14;  oxide, 
424. 

URANOCHALCITE,  mineral,  424. 

USEFUL  BOOKS,  list  of,  428. 


V 


VALUES  OF  GOLD  AND  SILVER, 
table  of,  444. 

VANADATE,  OF  LEAD,  425 ;  and 
zinc,  425. 

VANADIUM,  element,  14;  color  in 
scorifier,  191. 

VAN  WAGENEN'S  HYDRAULIC 
MINING,  433. 

VARIEGATED  COPPER  ORE  or  py- 
rites, 232,  299,  422. 

VAUQUELINITE,  mineral,  425,  427. 

"VEGETATING,"  2O7- 

VESSELS,  platinum,  127. 
VITREOUS  COPPER,  232,  298,  423; 
silver,  418. 


486 


INDEX. 


VITRIOL,  blue,  423;  copper,  423; 

green,    149;    lead,  425;  oil  of, 

151- 
VOLUMETRIC  ANALYSIS,  of  copper 

ore,  343;  Hart's,  430;  Button's, 

430. 

W 

WADE'S  MINING  LAW,  436. 

WAGNER'S  CHEMICAL  TECHNOLO- 
GY, 428. 

WASH-BOTTLE,  112. 

WASH,  CHALK,  152. 

WATCH-GLASSES,  112. 

WATER,  ammonia,  144;  distilled, 
chlorine  in,  142;  lime,  147;  re- 
agent, 142;  sulphuretted  hydro- 
gen, 149. 

WATTS'  DICTIONARY  OF  CHEMIS- 
TRY, 428. 

WEHRLITE,  mineral,  418,  421 

WEIGHING  gold  and  silver  beads, 
183,209;  gold  and  silver  beads, 
balances  for,  44;  gold  residues, 
183,  215. 

WEIGHTS,  59;  and  measures, 
Egleston's  and  Oldberg's,  435 ; 
apothecaries' tables,  446;  assay 
ton,  60;  assay  ton,  explana- 
tion of.  60;  assay  ton,  in 
grammes,  grains,  etc.,  450; 
avoirdupois,  tables.  445;  avoir- 
dupois to  troy,  399;  equivalents 
of  French  and  English,  449; 
French,  metric  or  gramme,  59; 
French  or  metric  tables,  447 ; 


"gold,"  64;  grain,  64;  tables 
of,  446 ;  troy  tables,  401 ;  troy 
to  avoirdupois,  401. 

WET  RE-AGENTS  FOR  ASSAYING, 
142. 

WHEAT  FLOUR,  133,  134. 

WHITE  LEAD  ORE,  312,  425;  re- 
agent, 141. 

WHITE  SUGAR,  134,  162. 

WHITNEYITE,  mineral,  425. 

WILLIAMS'  CHEMICAL  MANIPULA- 
TIONS, 430. 

WILSON'S  MINING  LAWS  OF  THE 
U.  S.,  436. 

WINDOW  GLASS,  as  re-agent,  137. 

WIRE,  gauze,  122;  gold,  167,  417; 
iron,  re-agent,  141 ;  silver,  419; 
stirring,  261;  triangle,  121. 

WOHLER'S  MINERAL  ANALYSIS, 
429. 

WOOD  CHARCOAL,  properties,  135; 
re-agent,  135;  reducing  power, 

134- 
WORK,  order  of,  in  scorificatfon 

process,  183. 
WULFINITE,  mineral,  427. 


YELLOW,  lead  ore  or  spar,  427, 
oxide  of  lead,  mineral,  426; 
oxide  of  lead,  re-agent,  139; 
prussiate  of  potash,  re-agent, 
147;  tellurium,  417,  420. 

YTTERBIUM,  element,  14. 

YTTRIUM,  element,  14. 


INDEX. 


487 


ZINC,  and  copper  carbonate,  422; 
and  lead  vanadate,  425;  blende, 
argentiferous,  170,  231,  249; 
color  on  cupel,  192,  color  of 
vapors,  235;  element,  14;  in 


battery,  148;  in  copper  ores, 
347,  350;  metal,  16;  metallic, 
re-agent,  148;  qualitative 
scheme  for,  240;  sifting-pans, 
35;  sulphide  or  sulphuret,  170, 
231,  232. 
ZIRCONIUM,  element,  14. 


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